The telomere-linked helicase (TLH) gene family in Magnaporthe oryzae: revised gene structure reveals a novel TLH-specific protein motif.

Telomere-linked RecQ helicase (TLH) genes have been identified in several fungi, where they occur as small gene families with each member copy residing within ~10 kb of a telomere. Here we describe the characterization of all 11 TLH gene copies in the reference strain of the fungus Magnaporthe oryzae. A consensus gene prediction revealed that the previously reported TLH1 gene is actually a mutated copy, and the full-length gene is almost two times longer. Only four full-length TLH genes were present in the strain that was analyzed, with the remaining copies containing premature stops caused by point mutations, indels, transposon insertions, and a telomere truncation. Interestingly, all of the TLH gene copies possessed numerous mutations indicative of the action of the repeat-induced point mutation process. However, there was evidence of purifying selection indicating maintenance of gene function. Alignment of full-length proteins from M. oryzae, Schizosaccharomyces pombe and M. anisopliae revealed the presence of a novel, highly conserved protein motif which suggests that the telomere-linked helicases have different functions and/or substrates to the RecQ helicases encoded by "internal" genes.