74] Microinjection of early SV40 DNA fragments and T antigen

Abstract

All early SV40 functions tested so far (Table I) are also detectable iin cells microinjected with the SV40 DNA fragment HpaII/BamHI A (map coordinates 0.16–0.735, Fig. 4). By contrast, fragments cut upstream of map position 0.16 have lost the ability to induce late gene expression (complementation of tsA virus at 41.5°), U antigen synthesis, or helper function for adenovirus 2. However, fragment BumI A, containing about 70% of the early coding region, still induces cellular DNA synthesis, whereas of all the functions tested, only intranuclear T antigen could be detected upon microinjection of the HpaII/HpaI B fragment.17,18 DNA sequences located at, or clockwise beyond the Bg/I cut (map position 0.67) seem to be required for correct intranuclear transcription, since the fragment Bg/I/BamHI failed to induce early SV40 functions in microinjected cells (Table I).17 However, cRNA transcribed from this fragment is translated into a protein(s) with SV40 T and U antigen specificity and the capacity to stimulate cell DNA synthesis following microinjection.