Expression of simian virus 40-rat preproinsulin recombinants in monkey kidney cells: use of preproinsulin RNA processing signals.

The complete rat preproinsulin gene I was cloned into a simian virus 30 (SV 40) vector. Most of the late region of the viral vector, including the SV40 intervening sequences (introns) and all of the major splice junctions, was deleted and replaced by the entire rat insulin gene. The recombinant molecules and a temperature-sensitive helper virus (tsA28) were inoculated into monkey kidney cultures. The formation of stable transcripts of the insulin insert was as efficient as the production of late SV40 mRNA. Analysis of these transcripts indicated that the rat preproinsulin gene nucleotide signals involved in RNA splicing and poly(A) addition were used. Examination of the 5' ends of the mRNAs showed several classes, one of which was the same size as the authentic rat insulinoma mRNA. This suggests that a portion of the transcripts may be initiated or processed faithfully, or both, at their 5' ends within rat insulin sequences. Significant quantities of a protein identified as rat proinsulin were synthesized. Detection of most of the proinsulin in the tissue culture medium suggests that this protein was secreted.