ABSTRACT
A series of plasmids encoding native and modified sequences of the hepatitis B virus core antigen (HBcAg) was created. Analysis of the products generated by expression of the plasmid genomes in Escherichia coli showed that a polypeptide with primary structure identical to that deduced for native HBcAg forms particles in the bacterial cells which are indistinguishable from the native nucleocapsids in morphological and antigenic properties. Removal of the thirty-nine C-terminal amino acids which form a protamine-like domain caused insignificant impairment of the particle-forming process. Modification of the N-terminal region of the polypeptide showed that at least part of the structural determinant governing particle formation is localised between amino acid residues 3 and 11. When the plasmid genes were expressed in an E. coli cell-free transcription - translation system, polypeptides devoid of ten to twenty N-terminal amino acids were formed in addition to the full-length products. From the results obtained it is proposed that a protease digestion site situated within the region containing amino acid residues 10 - 20 plays a role in the formation of the HBe antigen.
Subject(s)
Hepatitis B Core Antigens/chemistry , Hepatitis B virus/chemistry , Peptides/chemistry , Amino Acid Sequence , Base Sequence , Escherichia coli/genetics , Genes, Viral , Hepatitis B Core Antigens/genetics , Hepatitis B virus/genetics , Molecular Sequence Data , Peptides/genetics , Plasmids , Protein Conformation , Structure-Activity RelationshipABSTRACT
A set of plasmids carrying different initiator codons--either AUG, or GUG, or UUG, or CUG (as a control) in the hybrid gene lacIZ--was constructed by using synthetic oligonucleotides. GUG and UUG codons were demonstrated to be 2-3 times less effective than AUG in translation initiation. Furthermore, the correlation between the efficiencies of different initiator codons in translation initiation proved to vary, depending on the phase of bacterial growth. The rarely occurring usage in nature of the initiator codons GUG and UUG is supposed to be due to the particular role played by the initiator triplets in regulation of gene expression.
