The alpha- and beta-tubulins of Toxoplasma gondii are encoded by single copy genes containing multiple introns.

We have studied the fundamentals of gene expression in the protozoan parasite Toxoplasma gondii by analyzing, in detail, the genes encoding alpha- and beta-tubulin. Southern analysis and quantitation studies reveal that, unlike in other organisms studied thus far, both these genes are present as single copies in the haploid Toxoplasma genome. Sequencing of these genes indicates that they both contain multiple introns with conserved 5' and 3' splice site signals. We have found that HeLa cell nuclear extracts are able to accurately splice a Toxoplasma pre-mRNA construct. We have mapped, for the alpha-tubulin gene, the exact site of transcription initiation and the approximate site of poly A addition by primer extension and RNase protection assays. Trans-splicing, as demonstrated in the Kinetoplastida, is not involved in the formation of the mature alpha-tubulin transcript in T. gondii.