Biology subjects

Ma, C.-H.

Publications and source records attributed to Ma, C.-H..

3 recordsLinked to original sources

bioRxiv2023

The selfish yeast plasmid exploits a SWI/SNF-type chromatin remodeling complex for hitchhiking on chromosomes and ensuring high-fidelity propagation

Extra-chromosomal selfish DNA elements can evade the risk of being lost at every generation by behaving as chromosome appendages, thereby ensuring high fidelity segregation and stable persistence in host cell populations. The yeast 2-micron plasmid and episomes of the mammalian gammaherpes and papilloma viruses that tether to chromosomes and segregate by hitchhiking on them exemplify this strategy. We document for the first time the utilization of a SWI/SNF-type chromatin remodeling complex as a conduit for chromosome association by a selfish element. One principal mechanism for chromosome tethering by the 2-micron plasmid is the bridging interaction of the plasmid partitioning proteins (Rep1 and Rep2) with the yeast RSC2 complex and the plasmid partitioning locus STB. We substantiate this model by multiple lines of evidence derived from genomics, cell biology and interaction analyses. We describe a Rep-STB bypass system in which a plasmid engineered to non-covalently associate with the RSC complex mimics segregation by chromosome hitchhiking. Given the ubiquitous prevalence of SWI/SNF family chromatin remodeling complexes among eukaryotes, it is likely that the 2-micron plasmid paradigm or analogous ones will be encountered among other eukaryotic selfish elements.

molecular biology↗

bioRxiv2020

Disintegration promotes proto-spacer integration by the Cas1-Cas2 complex

Disintegration--the reversal of transposon DNA integration at a target site--is regarded as an abortive off-pathway reaction. Here we challenge this view with a biochemical investigation of the mechanism of protospacer insertion by the Streptococcus pyogenes Cas1-Cas2 complex, which is mechanistically analogous to DNA transposition. In supercoiled target sites, the predominant outcome is the disintegration of one-ended insertions that fail to complete the second integration event. In linear target sites, one-ended insertions far outnumber complete proto-spacer insertions. The second insertion event is most often accompanied by disintegration of the first, mediated either by the 3-hydroxyl exposed during integration or by water. One-ended integration intermediates may mature into complete spacer insertions via DNA repair pathways that are also involved in transposon mobility. We propose that disintegration-promoted integration is functionally important in the adaptive phase of CRISPR-mediated bacterial immunity, and perhaps in other analogous transposition reactions.

biochemistry↗

bioRxiv2020

Hitchhiking on condensed chromatin promotes plasmid persistence in yeast without perturbing chromosome function

Equipartitioning by chromosome hitchhiking and copy number correction by DNA amplification are at the heart of the evolutionary success of the selfish yeast 2-micron plasmid. The present analysis reveals plasmid presence near centromeres and telomeres in mitotic cells, with a preference towards the latter. The observed correlation of plasmid missegregation with non-disjunction of rDNA and telomeres under Cdc14 inactivation, higher plasmid missegregation upon induced missegregation of chromosome XII but not chromosome III, requirement of condensin for plasmid stability and the interaction of the condensin subunit Brn1 with the plasmid partitioning system lend functional credence to condensed chromatin being favored for plasmid tethering. By homing to condensed/quiescent chromosome locales, and not over-perturbing genome homeostasis, the plasmid may minimize fitness conflicts with its host. Analogous persistence strategies may be utilized by other extrachromosomal selfish genomes, for example, episomes of mammalian viruses that also hitchhike on host chromosomes for their stable maintenance.

cell biology↗