Comparative analysis of primary structure of the enzymes of dolichol cycle, yeast GDP-Man:Dol-PP-GlcNAc2 beta-mannosyltransferase (product of ALG1 gene) and yeast GDP-Man:Dol-PP-GlcNAc2Man2 alpha-1,3-mannosyltransferase (product of ALG2 gene) was conducted. In amino acid sequence of ALG2 protein extensive symmetrical segments were identified, in particular, 230-452 segment symmetrical relatively to Lys 346. Besides, repeated segments, homologous to the ones earlier identified by us in ALG1 protein were revealed in the molecule of ALG2 protein. The analysis of secondary structure of ALG2 protein allowed to reveal sites capable for forming alpha-helices with heptade periodicity. These helices can be included in formation of coifed-coifed structures. Similar structures were revealed earlier in the molecule of ALG1 protein. For sites able for formation of alpha-helices and neighbouring sites there was shown high homology of primary structure observed by us both at the comparison of ALG1 and ALG2 with each other and at the comparison with other enzymes of dolichol cycle. The data obtained point to evolutionary relationship between dolichol-coupled enzymes and in particular, between mannosyltransferases and dolicholphosphomannosylsynthase, using the same substrate GDP-mannose.