The intein of the Thermoplasma A-ATPase A subunit: Structure, evolution and expression in E. coli

Alireza G Senejani¹ , Elena Hilario² and J Peter Gogarten³

¹Department of Molecular and Cell Biology, University of Connecticut, Storrs, CT 06269-3044, USA

²Current address: HortResearch, 120 Mt Albert Road, Private Bag 92, 169 Mt Albert, Auckland, New Zealand

³Department of Molecular and Cell Biology, University of Connecticut, 75 North Eagleville Rd. Storrs, CT 06269-3044, USA

author email corresponding author email

BMC Biochemistry 2001, 2:13doi:10.1186/1471-2091-2-13


Published:	14 November 2001

Abstract

Background

Inteins are selfish genetic elements that excise themselves from the host protein during post translational processing, and religate the host protein with a peptide bond. In addition to this splicing activity, most reported inteins also contain an endonuclease domain that is important in intein propagation.

Results

The gene encoding the Thermoplasma acidophilum A-ATPase catalytic subunit A is the only one in the entire T. acidophilum genome that has been identified to contain an intein. This intein is inserted in the same position as the inteins found in the ATPase A-subunits encoding gene in Pyrococcus abyssi, P. furiosus and P. horikoshii and is found 20 amino acids upstream of the intein in the homologous vma-1 gene in Saccharomyces cerevisiae. In contrast to the other inteins in catalytic ATPase subunits, the T. acidophilum intein does not contain an endonuclease domain.

T. acidophilum has different codon usage frequencies as compared to Escherichia coli. Initially, the low abundance of rare tRNAs prevented expression of the T. acidophilum A-ATPase A subunit in E. coli. Using a strain of E. coli that expresses additional tRNAs for rare codons, the T. acidophilum A-ATPase A subunit was successfully expressed in E. coli.

Conclusions

Despite differences in pH and temperature between the E. coli and the T. acidophilum cytoplasms, the T. acidophilum intein retains efficient self-splicing activity when expressed in E. coli. The small intein in the Thermoplasma A-ATPase is closely related to the endonuclease containing intein in the Pyrococcus A-ATPase. Phylogenetic analyses suggest that this intein was horizontally transferred between Pyrococcus and Thermoplasma, and that the small intein has persisted in Thermoplasma apparently without homing.