The RNA genome of potato spindle tuber viroid (PSTV) is transcribed in vitro 
into complementary DNA and RNA by DNA-dependent DNA polymerase I and RNA 
polymerase, respectively, from Escherichia coli. In vitro synthesis of 
complementary RNA produces distinct transcripts larger than unit length thus 
reflecting the in vivo mechanism of viroid replication. The influence of varying 
experimental conditions on the transcription process is studied; actinomycin D 
is found to drastically reduce complementary RNA synthesis from the PSTV RNA 
template by RNA polymerase.