We are studying mcm (minichromosome maintenance) mutants of yeast
whichdestabilize small circular minichromosomes, each carrying an
ARS(autonomously replicating sequence) and CEN (centromere) DNA.
It wasexpected that these mutants would carry lesions in genes whose
products act in trans at ARS or CEN sequences of minichromosomal
DNA to impair its replication and/or segregation. This search, in
earlier work, had identified many genes which affect DNA replication.
We have been working with these mutants, with emphasis on one mutant,
mcm2. Using mitotic stability assays we have shown that this mutant
affects plasmid and chromosomal DNA replication by causing underinitiations
at their replication origins, leading to DNA damage at chromosomes
and their subsequent loss from the cells.
We have also undertaken a study of other mcm mutants which do not
affectDNA replication. We have cloned several MCM (MCM16, MCM17,
MCM18, MCM19,MCM21 and MCM22) genes which belong to the ARS-nonspecific
class of MCM mutants. We have shown that all of these genes are
required for chromosome segregation. MCM17 is the same as CHL4/CTF17
and MCM18 defines the same ORF as CTF19. Further work is directed
towards the characterzation of these genes to determine the molecular
mechanisms which govern chromosome stability in yeast.
Important publications (eight)
- Ghosh SK, Poddar A, Hajra S, Sanyal K, Sinha P (2001) The IML3/MCM19
gene of S. cerevisiae is required for a kinetochore related process
of chromosome segregation. Mol. Gen. Genet. (in press).
- Poddar A, Roy N. and Sinha P. (1999) MCM21 and MCM22, two novel
genes of theyeast Saccharomyces cerevisiae are required for chromosome
transmission. Molecular Microbiology 31:349-360.
- Sanyal K., Ghosh S.K. and Sinha P. (1998) The MCM16 gene of
the yeast Saccharomyces cerevisiae is required for chromosome
segregation, Mol. Gen. Genet 260:242-250.
- Gangopadhyay S.S., Ray S.S., Sinha P. and Lohia A. (1997) Unusual
genomeorganisation in Entamoeba histolytica leads to two overlapping
transcripts. Mol. Biochem. Parasitol. 89:73-83.
- Roy N, Poddar A, Lohia A and Sinha P. (1997) The mcm17 mutation
of yeast shows size-dependent segregational defect of a minichromosome.
Curr. Genet. 32:182-189.
- Ray A. and Sinha P. (1995) The mcm2 mutant of yeast causes DNA
damage with a requirement of RAD9 for repair. Curr. Genet. 27:95-101.
- Ray A., Roy N., Maitra M. and Sinha P. (1994). A 61 kb ring
chromosome shows ARS-dependent chromosome changes in its mitotic
stability in mcm2 mutant of yeast. Curr. Genet. 26:403-409
- Maiti A.K. and Sinha P. 1992. The mcm2 mutation of yeast affects
replication rather than segregation or amplification of the two
micron plasmid of yeast. J. Mol. Biol. 224: 545-558.
For M. Sc (II)
students of Biophysics, Molecular Biology and Genetics Dept., Calcutta Univ.
Rajabazar[the review by L. Guarente on Synthetic
enhancement in gene interaction (Trends in Genetics, 1993, vol. 9, 362-366).]