Genomic clones containing beta tubulin sequences were isolated from a lambda library of Drosophila melanogaster. In situ hybridization localized three genes to 56D and 60B on chromosome 2 as well as to 85D on chromosome 3. The latter was known through genetic analysis to be specifically expressed during spermatogenesis. The genomic clone, pTu85, derived from this region contains one complete beta tubulin coding region as well as the 3′ end of an additional so far unidentified beta tubulin gene. Genomic Southern hybridizations reveal a total of five fragments with beta tubulin homology. Clone pTu56 codes for an RNA of 1.8 kb which is expressed in all developmental stages. Clone pTu60 codes for a 2.5‐kb RNA expressed during embryogenesis and pupation. In testes RNA we detected a 2.2‐kb message homologous to pTu85.

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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.

Genomic clones of Drosophila melanogaster were isolated from a λ library by cross‐hybridization with the yeast gene coding for the 150‐kd subunit of RNA polymerase II. Clones containing a region of ∼2.0 kb with strong homology to the yeast gene were shown to code for a 3.9‐kb poly(A)+‐RNA. Part of the coding region was cloned into an expression vector. A fusion protein was obtained which reacted with an antibody directed against RNA polymerase II of Drosophila. Peptide mapping of the fusion protein yielded a number of spots identical with spots derived from the 140‐kd subunit of Drosophila RNA polymerase II. Sequence comparison of a segment of the Drosophila and the corresponding yeast clone yielded a high degree of homology at the protein level also, suggesting that we had isolated the gene coding for the 140‐kd subunit of RNA polymerase II from Drosophila. In situ hybridization localized the DmRP140 gene at 88 A/B on chromosome 3 while the DmRP215 gene has previously been localized at 10 C on the X chromosome. Analysis of the transcripts (7.0 and 3.9 kb) in female and male flies shows dosage compensation for the transcription of the DmRP215 gene.

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