The relatively large beta-tubulin gene family of Arabidopsis contains a member with an unusual transcribed 5′ noncoding sequence

We have characterized the beta-tubulin gene family of Arabidopsis thaliana. Five distinct genes were cloned and analyzed by restriction enzyme mapping and cross-hybridization studies. Three of the genes appear to be dispersed, whereas two others are linked within 1.5 kb of one another. The two linked genes are closely related and appear to have resulted from a fairly recent duplication. The three dispersed genes do not cross-hybridize to one another or to the two linked genes under highly stringent hybridization conditions, suggesting that they arose from more ancient duplications. From Southern analysis we estimate that there are a total of between six and ten beta-tubulin genes in Arabidopsis. Additional analyses indicate that the gene family is equal in size or larger than those in other plants, but significantly smaller than those in related Brassica species. Sequence determination of one of the Arabidopsis genes revealed a highly unusual transcribed leader sequence. The leader contains two fairly long tracks of adenines. One is located toward the 5′ end of the mRNA and the other is just before the initiation codon. A track of uridines is located between the adenine tracks. This leader can form two different secondary structures that may have regulatory significance.