Restriction of frog virus 3 polypeptide synthesis to immediate early and delayed early species by supraoptimal temperatures.

Multiplication of frog virus 3 (FV 3) occurs in mammalian cells provided they are incubated at temperatures lower than 33 degrees. The expression of the viral genome at supraoptimal temperatures was followed by analyzing the polypeptides produced in CHO-infected cells and comparing with those obtained under restrictive conditions provoked by amino acid analogs or metabolic inhibitors. Late polypeptides were not detected at 33 degrees and the number of delayed early species decreased gradually with increasing temperatures consequently the synthesis of all delayed early proteins was not turned on in response to a unique event. At 37 degrees the synthesis was limited to the immediate early species, i.e., the proteins synthesized after cycloheximide reversal. Temperature shift experiments suggested that delayed early genes remained untranscribed at 37 degrees. Thus, incubation of FV 3-infected mammalian cells at 37 degrees provides a unique way of limiting viral synthesis to immediate early proteins without the side-effect provoked by inhibitors.