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

Bacteriophage X174 gene A encodes two proteins: the gene A protein and the smaller A* protein, which is synthesized from a translational start signal within the A gene in the same reading frame as the gene A protein. The gene A protein is involved in initiation, elongation and termination of rolling circle DNA replication. The role of the A* protein in the life cycle of X174, however, is unknown. Using oligonucleotide-directed mutagenesis a viable Xl74 mutant was constructed in which the ATG start codon of the A* protein was changed into an ATT codon. This mutant, X-4499T, does not synthesize A* protein. The burst size of X-4499T amounted to 50% of that of wild type XI74. This indicates that A* protein, although advantageous for phage reproduction, is not essential during the life cycle of bacteriophage X174

A* protein of bacteriophage [phi]X174 carries an oligonucleotide which it can transfer to the 3-OH of a DNA chain

The bacteriophage φX174 gene A encodes two proteins: gene A protein and A* protein. Purified A* protein acts as a single-stranded, DNA-specific endonuclease which remains covalently attached to the 5′-end of the cleavage site. Incubation of A* protein with the synthetic heptamer CAACTTG or with oligonucleotides which yield this heptamer after cleavage with the A* protein yields oligonucleotides with the sequences CAACTTGAG, CAACTTGAGG and CAACTTGAGGA. This indicates that A* protein carries an oligonucleotide with the sequence -AG, AGG or -AGGA. The oligonucleotide can be transferred to the 3′-end of the heptamer CAACTTG. This suggests that A* protein reacts with a specific DNA sequence in the infected cell. Author Keywords: Bacteriophage φX174; A* protein; DNA—protein complex; Synthetic oligonucleotide; DNA-ligating activit

The bond in the bacteriophage øX174 gene A protein-DNA complex is a tyrosyl-5'-phosphate ester

AbstractThe bacteriophage øX174 gene A protein cleaves the viral strand of the double-stranded replicative form (RF) DNA of the phage at a specific site, the origin. It leaves a free 3'-OH at nucleotide 4305 (G) of the øx DNA sequence and binds covalently to the DNA. The nature and position of the covalent bond have been determined using the octadecadesoxyribonucleotide CAACTTG[32P]ATATTAATAAC. This octadecamer, which corresponds to nucleotides 4299–4316 of øX viral DNA, is cleaved by gene A protein. Gene A protein is bound to the labelled phosphate via a tyrosyl residue, indicating that binding occurs to the nucleotide corresponding to 4306 (A) of the øX viral DNA strand.Bacteriophage øX174Gene A proteinDNA replicationProtein-DNA complexSynthetic oligonucleotideTyrosyl-5'-phosphate este