Four unique genes required for beta tubulin expression in vertebrates.

We have isolated the four separate segments of chicken DNA which contain sequence homology to beta tubulin. With the exception of a fifth region of DNA which appears to contain only a 5' fragment of a beta gene, these four cloned sequences represent all of the beta tubulin encoding DNA in the chicken. Each gene is very similar in structure, containing three or four small intervening sequences clustered in the 5' portion of the coding region. Using RNAs prepared from a variety of cell lines and tissues, we have found five different mRNAs which carry beta tubulin sequences, two of which are encoded by the same gene. Three of these mRNAs are unexpectedly long (between 3500 and 4000 bases). However, these large mRNAs do give authentic beta tubulin translation products. Overall, we conclude that each of the four beta tubulin genes is a functional gene which is expressed in a specific program during differentiation. These data strongly suggest that four beta tubulins are necessary for proper microtubule function in vertebrates.