A 5' spliced leader is added in trans to both alpha- and beta-tubulin transcripts in Trypanosoma brucei.

The approximately 15 alpha- and 15 beta-tubulin genes of Trypanosoma brucei are arranged in a tandem array of alternating alpha- and beta-tubulin genes. We have examined the structure of mRNA transcripts from the tubulin gene family and have found at the 5' ends of both alpha- and beta-tubulin messages a 35-nucleotide spliced leader (SL) identical to that identified previously on the 5' ends of variant surface glycoprotein (VSG) mRNAs. No 35-nucleotide SL sequences were encoded in the tubulin intergenic regions; instead, the SL sequence apparently originates from small RNA transcripts encoded at sites that are unlinked to the tubulin genes. The tandem arrangement of the tubulin genes and the presence of the SL at the 5' end of both alpha- and beta-tubulin transcripts establishes that RNA joining between the SL and tubulin mRNA occurs in trans.