Persistence of phage lambda DNA in genomes of mouse cells transformed by lambda-carrying SV40 vectors

Morphological method for estimation of simian virus 40 infectious titer

The cytomorphologic method previously reported for titration of adenoviruses has been employed for estimating the infectious titer of simian virus 40 (SV 40). Infected cells forming intranuclear inclusions were determined. The method examined possesses a number of advantages over virus titration by plaque assay and cytopathic effect. The virus titer estimated by the method of inclusion counting and expressed as IFU/ml (Inclusion Forming Units/ml) corresponds to that estimated by plaque count and expressed as PFU/ml.

Construction of a specific amber codon in the simian virus 40 T-antigen gene by site-directed mutagenesis

The site-directed bisulfite mutagenesis technique has been used to construct a specific mutation, am404, at nucleotide position 3124 in the simian virus 40 genome. The mutation was contained within a PstI restriction site (map position 0.27) and prevented cleavage by PstI at that position. Nucleotide sequence analysis of the mutagenized region indicated that only a single base pair change had occurred: a guanosine x cytosine leads to adenine x thymine transition. Comparison of the nucleotide sequence of am404 with the known DNA sequence of simian virus 40 indicted that the mutation in am404 resulted in the conversion of a glutamine codon to an amber codon. am404 could not replicate autonomously when transfected into monkey cells (BSC-40) but did replicate when it was cotransfected with the late deletion helper virus dl1007. On the basis of its position in the T-antigen, gene am404 should produce a T-antigen 24% shorter than the wild-type protein.

Construction of an SV40-derived cloning vector

A new reiterated variant of simian virus 40 (SV40; dl1142) has been constructed. It should be useful for the purpose of cloning foreign pieces of DNA in SV40 virions. Up to 80% of the SV40 genome has been made available for substitution with foreign DNA and the vector contains a number of unique (single-cut) restriction sites which will facilitate cloning. The 5' and 3' regions of both the SV40 early and late messenger RNAs are included in the vector. Prokaryotic DNA has been successfully cloned in the early region of the vector. The transcriptional properties of the recombinant have been studied, and it was found that both the vector and insert DNA are transcribed, mainly as non-adenylated RNA.

On procaryotic gene expression in eucaryotic systems

Numerous types of interaction between pro- and eucaryotes exist in nature, from the endosymbiosis of some bacteria with unicellular organisms and insects to the complex systems of bacterial flora associated with the skin and intestines of animals and man, and nitrogen-fixation and crown-gall tumor induction in plants. Until recently, such interactions were not thought to include genetic transfer, but an increasing body of evidence points to the probability of similar naturally-occurring exchanges with wide-ranging implications for evolution and genetic manipulation. Experiments to elucidate the possible effects of procaryotic genes in eucaryotic systems have included in vitro and in vivo studies with both plant and animal systems, for instance the translation of bacterial messenger RNAs in the wheat germ and rabbit reticulocyte systems and the introduction of bacterial genes into plant protoplasts, animal cells and whole organisms. In the present paper we have tried to summarize the results of experiments involving the uptake, replication, transcription, translation and integration of procaryotic genes in various eucaryotic systems and to discuss the implications of such findings for basic research as well as for possible biomedical applications. Awareness of the possibility of procaryotic-eucaryotic genetic interactions may help to elucidate unresolved questions in pathology, such as possible involvement of the intestinal flora in carcinogenesis, as well as to provide valuable probes of eucaryotic control mechanisms and new approaches in agricultural genetic engineering.