Abstract
Reverse transcriptase (RT; RNA-dependent DNA nucleotidyltransferase) from Rauscher leukemia virus is synthesized in infected cells by way of a read-through poly- rotein of 200,000 molecular weight. This polyprotein (Pr200
gag-pol
) was precipitated by antiserum to RT; in a previous study all the monospecific antisera to
gag
proteins recognized Pr200
gag-pol
. Pr200
gag-pol
contains both p30 and RT peptide sequences. Intermediate RT-related precursors of 145,000 (Pr145
pol
), 135,000 (Pr135
pol
), and 125,000 (Pr125
pol
) molecular weights were specifically recognized by precipitation from infected cell extracts by antiserum to RT. These proteins shared methionine-containing tryptic peptide sequences with a virion polypeptide of 80,000 molecular weight (p80
pol
) precipitate by antiserum to RT. Purification of active RT enzyme from virions labeled with [
3
H]methionine showed that p80
pol
was the major component, based on analysis by gel electrophoresis and tryptic peptide mapping experiments. A polypeptide (Pr80
pol
), similar in size to mature viral p80
pol
, was also precipitated from infected cells by antiserum to RT. Its peptide map was nearly identical to that of virion p80
pol
. Pulse-chase studies showed that Pr80
pol
, Pr125
pol
, and Pr135
pol
were stable polypeptides, whereas Pr200
gag-pol
and Pr145
pol
were unstable precursors. Pulse-chase studies with the protein synthesis inhibitor, cycloheximide, showed that the processing of Pr200
gag-pol
occurred for a short time in the absence of protein synthesis.