title: The isolation, characterization and sequence of two divergent β-tubulin genes from soybean (Glycine max L.).
abstract: Two divergent β-tubulin genes (designated Sβ-1 and Sβ-2) were isolated by screening a soybean genomic library with a Chlamydomonas reinhardtii β-tubulin cDNA probe. Restriction fragment analysis of the clones recovered, and of soybean genomic DNA, indicated that these represent two unique classes of structurally different β-tubulin genes in the soybean genome. However, it is possible that unidentified members of these classes or additional highly divergent classes of β-tubulin genes (thus far undetected) exist in the soybean genome. The Sβ-1 and Sβ-2 genomic clones were sequenced, revealing that both are potentially functional genes which would encode β-tubulins of 445 and 449 amino acids, respectively. A comparison of their derived amino acid sequences with β-tubulins from several organisms showed that they are most homologous to Chlamydomonas β-tubulin (85-87%), with lesser degrees of homology to β-tubulins of vertebrate species (79-83%), Trypanosoma brucei (80-81%) and Saccharomyces cerevisiae (66-68%). The amino acid sequences of Sβ-1 and Sβ-2 are as divergent from each other as they are from the Chlamydomonas β-tubulin. The amino acids at the diverged positions in Sβ-2 are nearly all conservative substitutions while in Sβ-1, 18 of the 69 substitutions were non-conservative. Both soybean β-tubulin genes contain two introns in exactly the same positions. The first soybean intron is located in the same position as the third intron of the Chlamydomonas β-tubulin genes. Codon usage in the two soybean β-tubulins is remarkably similar (D (2)=0.87), but differs from codon usage in other soybean genes.
authors.affiliation: Department of Developmental and Cell Biology, University of California, 92717, Irvine, CA, USA.
authors.forename: M J
authors.initials: MJ
authors.lastname: Guiltinan
authors.forename: D P
authors.initials: DP
authors.lastname: Ma
authors.forename: R F
authors.initials: RF
authors.lastname: Barker
authors.forename: M M
authors.initials: MM
authors.lastname: Bustos
authors.forename: R J
authors.initials: RJ
authors.lastname: Cyr
authors.forename: R
authors.initials: R
authors.lastname: Yadegari
authors.forename: D E
authors.initials: DE
authors.lastname: Fosket