Spo11 is a meiosis-specific protein that is responsible for the initiation of recombination during the early stages of meiosis through the formation of DNA double-strand breaks (DSBs) by a type II DNA topoisomerase-like activity [, ]. These DSBs initiate homologous recombination, which is required for chromosomal segregation and generation of genetic diversity during meiosis. Spo11 acts in conjunction with several other proteins, including Rec102 in yeast, to bring about meiotic recombination []. Mouse and human homologues of Spo11 have been cloned and characterised. The proteins are 82% identical and share ~25% identity with other family members. Mouse Spo11 has been localised to chromosome 2H4, and human SPO11 to chromosome 20q13.2-q13.3, a region amplified in some breast and ovarian tumours [].Similarity between SPO11 and archaebacterial TOP6A proteins points to evolutionary specialisation of a DNA-cleavage function for meiotic recombination []. Note that the yeast SPO11 protein shares far less similarity to other SPO11 proteins than the human and mouse homologues do to each other.
Spo11 is a meiosis-specific protein that is responsible for the initiation of recombination during the early stages of meiosis through the formation of DNA double-strand breaks (DSBs) by a type II DNA topoisomerase-like activity [, ]. These DSBs initiate homologous recombination, which is required for chromosomal segregation and generation of genetic diversity during meiosis. Spo11 acts in conjunction with several other proteins, including Rec102 in yeast, to bring about meiotic recombination []. Mouse and human homologues of Spo11 have been cloned and characterised. The proteins are 82% identical and share ~25% identity with other family members. Mouse Spo11 has been localised to chromosome 2H4, and human SPO11 to chromosome 20q13.2-q13.3, a region amplified in some breast and ovarian tumours [].Similarity between SPO11 and archaebacterial TOP6A proteins points to evolutionary specialisation of a DNA-cleavage function for meiotic recombination []. Note that the yeast SPO11 protein shares far less similarity to other SPO11 proteins than the human and mouse homologues do to each other.
MTOPVIB (meiotic topoisomerase VIB-like) is a structural homologue of the archaeal topo VIB subunit []. MTOPVIB forms a complex with the two Arabidopsis thaliana SPO11 orthologues (SPO11-1 and SPO11-2) and is essential for meiotic DSB formation []. The SPO11 protein catalyzes the formation of meiotic DNA double strand breaks (DSBs) and it is the eukaryotic homologue of the archaeal DNA topoisomerase VIA.
This family of animal proteins is known as TOPOVIB-like as it shares strong structural similarity to the TopoVI DNA topoisomerase subunit B. TOPOVIB-like interacts and forms a complex with SPO11 and is required for meiotic DNA double-strand break formation []. TOPOVIB-like may be involved in the regulation of DNA cleavage.
This entry represents Spo11, a meiotic recombination protein found in eukaryotes, and subunit A of topoisomerase VI, a type IIB topoisomerase found predominantly in archaea [, , , ]. These two types of proteins share structural homology.DNA topoisomerases regulate the number of topological links between two DNA strands (i.e. change the number of superhelical turns) by catalysing transient single- or double-strand breaks, crossing the strands through one another, then resealing the breaks. They can be divided into two classes: type I enzymes (, topoisomerases I, III and V) break single-strand DNA, and type II enzymes (, topoisomerases II, IV and VI) break double-strand DNA []. Topoisomerase VI is a type IIB enzymes that assembles as a heterotetramer, consisting of two A subunits required for DNA cleavage and two B subunits required for ATP hydrolysis. The B subunit is structurally similar to the ATPase domain of type IIA topoisomerases, but the A subunit is distinct, and instead shares homology with the Spo11 protein. Spo11 is a meiosis-specific protein that is responsible for the initiation of recombination through the formation of DNA double-strand breaks by a type II DNA topoisomerase-like activity. Spo11 acts in conjunction with several other proteins, including Rec102 in yeast, to bring about meiotic recombination [].
This entry represents Spo11, a meiotic recombination protein found in eukaryotes, and subunit A of topoisomerase VI, a type IIB topoisomerase found predominantly in archaea [, , , ]. These two types of proteins share structural homology.DNA topoisomerases regulate the number of topological links between two DNA strands (i.e. change the number of superhelical turns) by catalysing transient single- or double-strand breaks, crossing the strands through one another, then resealing the breaks. They can be divided into two classes: type I enzymes (, topoisomerases I, III and V) break single-strand DNA, and type II enzymes (, topoisomerases II, IV and VI) break double-strand DNA []. Topoisomerase VI is a type IIB enzymes that assembles as a heterotetramer, consisting of two A subunits required for DNA cleavage and two B subunits required for ATP hydrolysis. The B subunit is structurally similar to the ATPase domain of type IIA topoisomerases, but the A subunit is distinct, and instead shares homology with the Spo11 protein. Spo11 is a meiosis-specific protein that is responsible for the initiation of recombination through the formation of DNA double-strand breaks by a type II DNA topoisomerase-like activity. Spo11 acts in conjunction with several other proteins, including Rec102 in yeast, to bring about meiotic recombination [].
Rec104 is one of several meiosis specific genes required for generating meiotic DSBs (double strand breaks) []. It is suggested that Rec102 and Rec104 directly promote DSB formation as part of a multiprotein complex with Spo11. Rec102 and Rec104 are mutually dependent for proper sub-cellular localization, and share a requirement for Spo11 and Ski8 for their recruitment to meiotic chromosomes. Moreover, Rec102 is required for Rec104 to accumulate to normal steady-state levels and to be properly phosphorylated. It is likely that Rec102 and Rec104 move freely in and out of the nucleus but are most stably sequestered there only when they can form a complex on chromosomes [].
This topoisomerase-primase (TOPRIM) nucleotidyl transferase/hydrolase domain is found in the type II topoisomerase VIA and Spo11. This subgroup contains proteins similar to Sulfolobus shibatae topoisomerase VIA (TopoVIA) []and Saccharomyces cerevisiae meiotic recombination factor Spo11 []. Type II DNA topoisomerases catalyze the ATP-dependent transport of one DNA duplex through another, in the process generating transient double strand breaks via covalent attachments to both DNA strands at the 5' positions. TopoVI enzymes are heterotetramers found in archaea and plants [, ]. Spo11 plays a role in generating the double strand breaks that initiate homologous recombination during meiosis [, ]. S. shibatae TopoVI relaxes both positive and negative supercoils, and in addition has a strong decatenase activity [].The TOPRIM domain has two conserved motifs, one of which centres at a conserved glutamate and the other one at two conserved aspartates (DxD). For topoisomerases, the conserved glutamate is believed to act as a general base in strand joining, and as a general acid in strand cleavage []. The DXD motif may co-ordinate Mg2+, a cofactor required for full catalytic function.
The representative of this plant family is PAIR1 (HOMOLOGOUS PAIRING ABERRATION IN RICE MEIOSIS1), a protein that plays an essential role in establishment of homologous chromosome pairing in meiosis. Mutations in the gene encoding this protein also affect spindle formation and sporulation []. This family also contains the Putative recombination initiation defects 3 (AtPRD3) involved in the meiotic recombination initiation [].In flowering plants, gametophyte formation relies on meiosis. In meiosis I, the homologous chromosomes are separated into two daughter cells. In meiosis II, the sister chromosomes are then separated into newly formed daughter cells. During prophase I, several events occurs: sister chromatid cohesion, homologous chromosome synapsis, recombination, crossover formation and chromosome segregation. Homologous recombination is initiated from the formation of DNA double-strand breaks (DSBs). The formation of DSBs is catalyzed by Spo11 and its homologues. So far, six Arabidopsis proteins, AtSPO11-1, AtSPO11-2, AtPRD1, AtPRD2, AtPRD3 and AtDFO, have been shown to be involved in DSB formation [].
This entry represent a group of plant proteins, including AtPRD1 from Arabidopsis. AtPRD1 is required for meiotic double strand break formation []. AtPRD1 is homologous to MEI1 of humans and mice and contains a conserved N-terminal region that can interact with AtSPO11-1 and itself [].In flowering plants, gametophyte formation relies on meiosis. In meiosis I, the homologous chromosomes are separated into two daughter cells. In meiosis II, the sister chromosomes are then separated into newly formed daughter cells. During prophase I, several events occurs: sister chromatid cohesion, homologous chromosome synapsis, recombination, crossover formation and chromosome segregation. Homologous recombination is initiated from the formation of DNA double-strand breaks (DSBs). The formation of DSBs is catalyzed by Spo11 and its homologues. So far, six Arabidopsis proteins, AtSPO11-1, AtSPO11-2, AtPRD1, AtPRD2, AtPRD3 and AtDFO, have been shown to be involved in DSB formation [].
This entry represent a group of plant proteins, including AtDFO from Arabidopsis. AtDFO is a plant-specific protein involved in DNA double-strand break formation during meiosis [].In flowering plants, gametophyte formation relies on meiosis. In meiosis I, the homologous chromosomes are separated into two daughter cells. In meiosis II, the sister chromosomes are then separated into newly formed daughter cells. During prophase I, several events occurs: sister chromatid cohesion, homologous chromosome synapsis, recombination, crossover formation and chromosome segregation. Homologous recombination is initiated from the formation of DNA double-strand breaks (DSBs). The formation of DSBs is catalyzed by Spo11 and its homologues. So far, six Arabidopsis proteins, AtSPO11-1, AtSPO11-2, AtPRD1, AtPRD2, AtPRD3 and AtDFO, have been shown to be involved in DSB formation [].
The spindle assembly checkpoint (SAC) ensures the fidelity of chromosome segregation. In plants, Msp1 (also known as AtPRD2) has been identified as one of the SAC components []. Msp1 is required for meiotic spindle organization []and DNA double-strand break formation [].In flowering plants, gametophyte formation relies on meiosis. In meiosis I, the homologous chromosomes are separated into two daughter cells. In meiosis II, the sister chromosomes are then separated into newly formed daughter cells. During prophase I, several events occurs: sister chromatid cohesion, homologous chromosome synapsis, recombination, crossover formation and chromosome segregation. Homologous recombination is initiated from the formation of DNA double-strand breaks (DSBs). The formation of DSBs is catalyzed by Spo11 and its homologues. So far, six Arabidopsis proteins, AtSPO11-1, AtSPO11-2, AtPRD1, AtPRD2, AtPRD3 and AtDFO, have been shown to be involved in DSB formation [].
DNA topoisomerases regulate the number of topological links between two DNA strands (i.e. change the number of superhelical turns) by catalysing transient single- or double-strand breaks, crossing the strands through one another, then resealing the breaks []. These enzymes have several functions: to remove DNA supercoils during transcription and DNA replication; for strand breakage during recombination; for chromosome condensation; and to disentangle intertwined DNA during mitosis [, ]. DNA topoisomerases are divided into two classes: type I enzymes (; topoisomerases I, III and V) break single-strand DNA, and type II enzymes (; topoisomerases II, IV and VI) break double-strand DNA [].Type II topoisomerases are ATP-dependent enzymes, and can be subdivided according to their structure and reaction mechanisms: type IIA (topoisomerase II or gyrase, and topoisomerase IV) and type IIB (topoisomerase VI). These enzymes are responsible for relaxing supercoiled DNA as well as for introducing both negative and positive supercoils [].This entry represents subunit B of topoisomerase VI, a type IIB topoisomerase found predominantly in archaea, but also in a few eukayotes, such as the plant Arabidopsis thaliana []. This enzyme assembles as a heterotetramer, consisting of two A subunits required for DNA cleavage and two B subunits required for ATP hydrolysis. The B subunit is structurally similar to the ATPase domain of type IIA topoisomerases, but the A subunit is distinct, and instead shares homology with the Spo11 protein that mediates double-strand DNA breaks during meiotic recombination in eukaryotes []. Therefore, though related to type IIA topoisomerases, topoisomerase VI may have a distinctive mechanism of action.
DNA topoisomerases regulate the number of topological links between two DNA strands (i.e. change the number of superhelical turns) by catalysing transient single- or double-strand breaks, crossing the strands through one another, then resealing the breaks []. These enzymes have several functions: to remove DNA supercoils during transcription and DNA replication; for strand breakage during recombination; for chromosome condensation; and to disentangle intertwined DNA during mitosis [, ]. DNA topoisomerases are divided into two classes: type I enzymes (; topoisomerases I, III and V) break single-strand DNA, and type II enzymes (; topoisomerases II, IV and VI) break double-strand DNA [].Type II topoisomerases are ATP-dependent enzymes, and can be subdivided according to their structure and reaction mechanisms: type IIA (topoisomerase II or gyrase, and topoisomerase IV) and type IIB (topoisomerase VI). These enzymes are responsible for relaxing supercoiled DNA as well as for introducing both negative and positive supercoils [].This entry represents subunit A of topoisomerase VI, a type IIB topoisomerase found predominantly in archaea, but also in a few eukayotes, such as the plant Arabidopsis thaliana []. This enzyme assembles as a heterotetramer, consisting of two A subunits required for DNA cleavage and two B subunits required for ATP hydrolysis. The B subunit is structurally similar to the ATPase domain of type IIA topoisomerases, but the A subunit is distinct, and instead shares homology with the Spo11 protein that mediates double-strand DNA breaks during meiotic recombination in eukaryotes []. The core of subunit A is a dimer, with a deep groove in which the DNA molecule is thought to bind, with the monomers separating during DNA transport. Therefore, though related to type IIA topoisomerases, topoisomerase VI may have a distinctive mechanism of action.
