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To construct the phylogenetic tree of S. cerevisiae S288C α glucosidases, we performed pairwise and multiple comparison of all ten catalytic domains of GH13 and GH31 families of this organism. For this purpose, we used standard methods of comparative analysis of amino acid sequences [15]. For domains encoded by genes YBR229c (GH31 family) and YPR184w (GH13_25 subfamily), we managed to obtain only short local alignments with the remaining eight domains. This is not striking because the GH13_25 subfamily is one of the most divergent (along with GH13_33), and it was proposed to be con sidered as an independent glycoside hydrolase family [14]. YIL172c and YJL221c proteins proved to be identical and were regarded as one protein. The remaining seven domains were used to construct mul tiple alignment and phylogenetic tree (figure). Analy sis also included the GH13 domain of Mal62 maltase of the S. cerevisiae ATCC56959 strain (isomaltase from S. cerevisiae ATCC56960 was identical to YGR287c and, for this reason, was not included into consideration). The GH13 domain, encoded by the YEL011w gene, was considered as an outgroup. Phy logenetic analysis demonstrated the existence of two distinctly isolated α glucosidase clusters (with a more than 99% bootstrap support). One of them combines three maltases; the other one, isomaltase and its three close paralogs. In the diagnostic site, all the three mal tases comprise the Thr–Ala–Gly tripeptide and four proteins from the isomaltase cluster Val–Gly–Ser.

The level of identity of amino acid sequences within these clusters does not exceed 99 and 92%, respec tively, and …