TAM1, A TELOMERE-ASSOCIATED MEIOTIC PROTEIN, FUNCTIONS IN CHROMOSOME SYNAPSIS AND CROSSOVER INTERFERENCE

The TAM1 gene of Saccharomyces cerevisiae is expressed specifically du ring meiosis and encodes a protein that localizes to the ends of meiot ic chromosomes. In a tam1 null mutant, there is an increase in the fre quency of chromosomes that fail to recombine and an associated increas e in homolog nondisjunction at meiosis I, The tam1 mutant also display s an increased frequency of precocious separation of sister chromatids and a reduced efficiency of distributive disjunction. The defect in d istributive disjunction may be attributable to overloading of the dist ributive system by the increased number of nonrecombinant chromosomes. Recombination is not impaired in the tam1 mutant, but crossover inter ference is reduced substantially. In addition, chromosome synapsis is delayed in tam1 strains. The combination of a defect in synapsis and a reduction in interference is consistent with previous studies suggest ing a role for the synaptonemal complex in regulating crossover distri bution. tam1 is the only known yeast mutant in which the control of cr ossover distribution is impaired, but the frequency of crossing over i s unaffected. We discuss here possibilities for how a telomere-associa ted protein might function in chromosome synapsis and crossover interf erence.