ИСТИНА

Rap1 is a major telomere-binding protein in most of the budding yeast species. At least in Saccharomyces cerevisiae it also regulates transcription of many genes, including genes of ribosomal proteins. Rap1 functions were studied in S. cerevisiae (and several related species from Saccharomycetaceae family) and in Candida albicans (a member of “CTG clade”). Thermotolerant methylotrophic budding yeast Hansenula polymorpha appears to have two homologues of Rap1 (HpRap1A and HpRap1B). Two RAP1 genes can also be found in other yeasts from the “methylotroph clade”, suggesting that RAP1 duplication occurred in their common ancestor. Here we present characterization of DNA binding properties of Rap1 homologues from H. polymorpha. We found that HpRap1A (but not HpRap1B) binds a short site (5’-GGTGTAGGGATGC-3’) within subtelomeric regions of H. polymorpha, which is similar to ScRap1 consensus and is almost identical to Rap1 recognition motif of Candida albicans. HpRap1B (but not HpRap1A) recognizes telomere sequence (5’‑GGGTGGCGGGGTGGCG-3’) with moderate specificity, indicating that it performs telomeric functions in H. polymorpha. Consistently, C-terminal truncations of HpRap1B (but not HpRap1A) protein lead to telomere overelongation. Interestingly, HpRap1B exhibits higher affinity towards telomeres from other “methylotrophs” in vitro. We also found that binding sites of both Rap1 homologues are present within promoters of different important genes (e.g. methanol oxidase in case of HpRap1A and several ribosomal proteins in case of HpRap1B), therefore Rap1 may take part in transcription regulation in methylotrophic yeasts. We believe that these findings are important for understanding evolution of telomere biology and Rap1 role in it.