Overlapping coding regions and trancriptional units of two essential chromosomal genes (CCT8, TRP1)in the fungal pathogen Candida albicans

Abstract

Sequencing of the 3'-untranslated region of the CCT8 gene of the fungal pathogen Candida albicans revealed that the CCT8 coding region overlaps 13 bp with the coding region of the convergently orientated TRP1 gene. The same overlap was found in three strains with different genetic backgrounds. 3'-RACE was used to determine that the CCT8 and TRP1 transcripts extended significantly into the coding region of the adjacent gene, which also contained sequences encoding the poly(A) addition site. A strain retaining one wild-type CCT8/TRP1 locus on one chromosome and a deletion on the other homologous chromosome contained both CCT8 and TRP1 transcripts; this result indicates that both transcripts are synthesized from the same gene locus. The CCT8/TRP1 gene pair of C . albicans constitutes an extreme natural case of transcriptional overlap in a eukaryote. The results confirm that convergent overlapping transcription units are compatible with expression of the overlapping genes.