Alteration of the ATG start codon of the A protein of bacteriophage phi X174 into an ATT codon yields a viable phage indicating that A protein is not essential for phi X174 reproduction

Molecular dissection of the replication system of plasmid pIGRK encoding two in-frame Rep proteins with antagonistic functions

BACKGROUND

Gene overlapping is a frequent phenomenon in microbial genomes. Excluding so-called "trivial overlapping", there are significant implications of such genetic arrangements, including regulation of gene expression and modification of protein activity. It is also postulated that, besides gene duplication, the appearance of overlapping genes (OGs) is one of the most important factors promoting a genome's novelty and evolution. OGs coding for in-frame proteins with different functions are a particularly interesting case. In this study we identified and characterized two in-frame proteins encoded by OGs on plasmid pIGRK from Klebsiella pneumoniae, a representative of the newly distinguished pHW126 plasmid family.

RESULTS

A single repR locus located within the replication system of plasmid pIGRK encodes, in the same frame, two functional polypeptides: a full-length RepR protein and a RepR' protein (with N-terminal truncation) translated from an internal START codon. Both proteins form homodimers, and interact with diverse DNA regions within the plasmid replication origin and repR promoter operator. Interestingly, RepR and RepR' have opposing functions - RepR is crucial for initiation of pIGRK replication, while RepR' is a negative regulator of this process. Nevertheless, both proteins act cooperatively as negative transcriptional regulators of their own expression.

CONCLUSIONS

Regulation of the initiation of pIGRK replication is a complex process in which a major role is played by two in-frame proteins with antagonistic functions. In-frame encoded Rep proteins are uncommon, having been described in only a few plasmids. This is the first description of such proteins in a plasmid of the pHW126 family.

Solid-phase synthesis of H-Phe-Tyr-(pATAT)-NH2: a nucleopeptide fragment from the nucleoprotein of bacteriophage phi X174

The preparation of the nucleopeptide H-Phe-Tyr-(pATAT)-NH2 could be realized via a solid phase phosphitetriester approach and by using the protected protecting group 2-(tert-butyldiphenylsilyoxymethyl)-benzoyl for the masking of the N6-amino function of deoxyadenosine. The latter protecting group can be removed under mild conditions with fluoride ion.

Synthesis of the nucleopeptides H-Phe-Tyr(pGC)-NH2 and H-Phe-Ser(pGC)-Ala-OH via a phosphotriester approach

Use of the protecting groups di-n-butylaminomethylene,2-nitrophenylsulfenyl and the ester of 2-(hydroxymethyl)-9,10-anthraquinone, enabled us for the first time to prepare nucleopeptide fragments containing 2'-deoxyguanosine and a free carboxylic acid group.