Both alpha-tubulin genes are transcriptionally active in Stylonychia lemnae

Macronuclear DNA of the hypotrichous ciliate Stylonychia lemnae contains two size-classes of molecules coding for alpha-tubulin. Analysis of their coding regions demonstrates that these two size-classes represent two different functional alpha-tubulin genes, alpha 1 and alpha 2; a comparison of these regions shows a 97% homology in their nucleotide sequence and 98.5% in their amino acid sequence. S1-mapping experiments indicate that both alpha 1- and alpha 2-tubulin genes are transcribed. The 5' and 3' noncoding regions flanking the alpha 1- and alpha 2-tubulin genes differ in both length and nucleotide sequence within one strain. When different strains are compared, however, identical non-coding regions and slightly varying coding regions can be found in DNA molecules containing the alpha 1-tubulin genes.