Tissue-specific and constitutive alpha-tubulin genes of Drosophila melanogaster code for structurally distinct proteins.

Theurkauf et al. (1986). Proc Natl Acad Sci USA DOI: 10.1073/pnas.83.22.8477 Citations: 156

Whether multiple tubulin genes encode distinct proteins was unclear, with no full family sequenced. This paper sequenced all four Drosophila alpha-tubulin genes and transcripts. Constitutive alpha1/alpha3 differed by two residues, while maternal alpha4 differed at 149 of 450.

Parts used

α1-Tubulin Promoter

Key findings

  • Complete sequencing of Drosophila α-tubulin genes α1 and α3 revealed constitutive expression patterns with 92% nucleotide sequence homology in coding regions. The encoded proteins differed by only two conservative amino acid substitutions at positions 170 and 305, with α1 showing 96% identity to porcine brain α-tubulin across 450 residues. Extended homology blocks spanning 120 nucleotides in the 5' untranslated leader regions suggested coordinate transcriptional or post-transcriptional regulation between the two genes.

  • The male-specific α2 gene encoded an α-tubulin differing from constitutive α1 at 21 of 450 amino acid positions with 87% nucleotide homology in coding sequences. Six nonconservative substitutions clustered within the 14 carboxyl-terminal residues represented a region previously implicated in microtubule assembly regulation and MAP interactions. Adult expression restricted to males suggested specialized function in flagellar axoneme assembly in Drosophila testes.

  • The maternal α4 gene produced the most divergent α-tubulin reported, differing from α1 at 149 of 450 positions with only 68% nucleotide homology. An 11-amino acid insertion between residues 34-61 and replacement of the universally conserved C-terminal tyrosine with phenylalanine distinguished α4 from all sequenced α-tubulins. Expression restricted to ovarian nurse cells and 0-3 hour embryos coincided with 13 rapid synchronous nuclear divisions averaging 9 minutes each during early Drosophila development.

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Abstract

We have determined the nucleotide sequences of all four Drosophila alpha-tubulin genes (alpha 1, alpha 2, alpha 3, and alpha 4). Two of the genes, alpha 1 and alpha 3, are constitutively expressed and code for proteins that are very similar to previously sequenced alpha-tubulins. They differ from each other by only two amino acid substitutions. These two genes also have blocks of homology between the noncoding leader regions of their transcription units. In contrast to these constitutive genes, the tissue-specific alpha 2 and alpha 4 genes code for tubulins with different structures. The alpha 2 mRNA is male-specific in adults and codes for a tubulin that differs from alpha 1 at 21 of the 450 residues. Six nonconservative substitutions are clustered within the 14 carboxyl-terminal amino acids, a region implicated in the regulation of microtubule assembly. The alpha 4 mRNA is maternal and is found only in ovarian nurse cells, eggs, and early embryos. It codes for the most highly divergent alpha-tubulin yet reported and differs from alpha 1 at 149 positions.