Production of a discrete, heterogeneous population of beta-galactosidase polypeptides using baculovirus expression...

Gel electrophoresis analysis of immunoprecipitated beta-galactosidase and polyhedrin-beta-galactosidase expressed in Spodoptera frugiperda cells infected with recombinant Autograph californica nuclear polyhedrosis virus revealed the existence of a population of discrete beta-galactosidase polypeptides. Several of the polypeptides observed in the fusion protein expression experiments exhibit a consistent pattern of slightly greater molecular weight when compared to the nonfusion beta-galactosidase that is compatible with the hypothesis that these fusion protein fragments retain the N-terminal polyhedrin residues. Pulse-chase experiments showed that overall beta-galactosidase degradation occurred at a negligible rate compared to the synthesis rate at 96 h postinfection, yet the fragments are observed for short pulse times. Degradation of several different beta-galactosidase polypeptides was observed 24 h postinfection. Ribonucleic acid hybridization analysis of lacZ transcripts shows significant heterogeneity that may result from premature transcription termination. Although a proteolytic origin cannot be excluded, the data assembled suggest that premature termination of transcription or translation is the likely cause for the heterogeneous population of immunoreactive peptides observed. Many discrete forms of beta-galactosidase polypeptides were also observed in studies with Escherichia coli, indicating that production of these heterogeneous forms is not a consequence of heterologous expression of the enzyme.