Testis-specific beta 2 tubulins are identical in Drosophila melanogaster and D. hydei but differ from the ubiquitous beta 1 tubulin.

In Drosophila as in many organisms beta tubulins are encoded by a gene family. We have determined the complete nucleotide sequences coding for the beta 1 and beta 2 tubulins of Drosophila melanogaster and the beta 2 tubulin of D. hydei, and found these insect beta tubulins to be highly conserved and like beta tubulins of other organisms. This is discussed with reference to the possible functional domains of these proteins. The beta 1 tubulin gene of Drosophila is constitutively expressed, whereas the beta 2 tubulin is expressed specifically in the testes. In D. melanogaster the amino acid sequences of these proteins are 95% homologous, differing at only 25 positions. In the testes the beta 2 tubulin participates in different microtubules as shown by genetic analysis (Kemphues et al. 1982). Interestingly, all of the amino acids characteristic of the testis-specific beta 2 tubulin are also present in the corresponding gene of D. hydei. Of special interest is the high degree of conservation of the carboxy-terminal domain in these functionally equivalent beta tubulins.