Differential expression of three alpha-tubulin genes in Chinese hamster ovary cells

Chinese hamster ovary cells contain a complex family of ca. 16 unique alpha-tubulin sequences and a similar multiplicity of beta sequences. To examine which members of this multigene family are expressed, we constructed cDNA libraries from two Chinese hamster ovary cell lines according to the method of H. Okayama and P. Berg (Mol. Cell. Biol. 3:280-289, 1983). Each library consisted of 5.5 X 10(5) transformants and contained a high percentage of full-length tubulin clones. Three different alpha-tubulin genes were identified by sequence analysis of the 3' noncoding regions of these tubulin clones. The relative abundance of the transcripts corresponding to the three genes was estimated by gene-specific dot blotting of 96 cDNA alpha-tubulin clones and was found to be 71, 24, and 5%. There is little homology in the 3' noncoding sequences of these genes; however, a strong interspecies homology exists in this region for two of the Chinese hamster ovary genes with the two alpha-tubulin genes previously described in other systems. The third Chinese hamster ovary gene, with an expression frequency of 24%, is unique in that its 3' noncoding region is unlike that of the other mammalian alpha-tubulin genes. In addition, limited sequence data from the coding region of this gene indicates it codes for a unique alpha-tubulin protein.