Reverse-transcriptase polymerase chain reaction cloning of the 3'-ends of the alpha-tubulin cDNAs of Tritrichomonas mobilensis in combination with Southern-blot analysis identified seven to eight distinct alpha-tubulin genes. All seven lack a carboxy-terminal tyrosine and the corresponding sequence compatible with posttranslational tyrosination. This indicates that whereas tyrosination of alpha-tubulin has been found in most species, including humans and trypanosomes, it is absent in trichomonads.