Ramírez-Zavaleta Candy Y, Salas-Delgado Griselda E, De Las Peñas Alejandro, Castaño Irene
Instituto Potosino de Investigación Científica y Tecnológica, San Luis Potosí SLP, Mexico.
Eukaryot Cell. 2010 Oct;9(10):1602-11. doi: 10.1128/EC.00129-10. Epub 2010 Jul 30.
Candida glabrata is a haploid opportunistic fungal pathogen that is phylogenetically related to Saccharomyces cerevisiae. Even though C. glabrata has no known sexual cycle, it contains, like S. cerevisiae, three mating type-like loci (MTL) called MTL1, MTL2, and MTL3, as well as most of the genes required for mating, meiosis, and sporulation. MTL1 is localized at an internal position on chromosome B and is thought to be the locus corresponding to the MAT locus in S. cerevisiae. MTL2 and MTL3 are localized close to two telomeres on different chromosomes (29.4 kb from Chr E-L and 10.5 kb from Chr B-L, respectively). By using URA3 reporter gene insertions at the three MTL loci, we found that in contrast to the case for S. cerevisiae, only MTL3 is subject to transcriptional silencing while MTL2 is transcriptionally active, and this is in agreement with previously reported data. We found that the silencing of MTL3 is nucleated primarily at the left telomere of chromosome B and spreads over 12 kb to MTL3, rather than nucleating at flanking, closely positioned cis-acting silencers, like those flanking HMR and HML of S. cerevisiae. Interestingly, the silencing of MTL3 absolutely requires the yKu70, yKu80, and Rif1 proteins, in sharp contrast to the silencing of the HM loci of S. cerevisiae. In addition, we found that several cell type-specific genes are expressed in C. glabrata regardless of the presence, or even absence, of mating type information at any of the MTL loci.
光滑念珠菌是一种单倍体机会性真菌病原体，在系统发育上与酿酒酵母相关。尽管光滑念珠菌没有已知的有性周期，但它像酿酒酵母一样，含有三个类似交配型的位点（MTL），分别称为MTL1、MTL2和MTL3，以及交配、减数分裂和孢子形成所需的大多数基因。MTL1位于染色体B的内部位置，被认为是与酿酒酵母中MAT位点相对应的位点。MTL2和MTL3分别位于不同染色体上靠近两个端粒的位置（分别距离染色体E-L的端粒29.4 kb和染色体B-L的端粒10.5 kb）。通过在三个MTL位点插入URA3报告基因，我们发现与酿酒酵母的情况不同，只有MTL3受到转录沉默，而MTL2具有转录活性，这与先前报道的数据一致。我们发现MTL3的沉默主要在染色体B的左末端起始，并延伸12 kb至MTL3，而不是像酿酒酵母的HMR和HML侧翼那样，在侧翼紧密定位的顺式作用沉默子处起始。有趣的是，MTL3的沉默绝对需要yKu70、yKu80和Rif1蛋白，这与酿酒酵母HM位点的沉默形成鲜明对比。此外，我们发现无论任何MTL位点是否存在交配型信息，甚至不存在交配型信息时，几种细胞类型特异性基因在光滑念珠菌中都有表达。
