The 3' ends of the S and M messenger RNAs isolated from BHK21 cells infected with Germiston virus were analyzed by mapping with RNase T2 or nuclease S1. The transcription termination signal was found to be located approximately 115 and 80 nucleotides upstream from the 3' end of the S and M genomic RNA templates, respectively. Both mRNAs were found to possess several adenosine residues at their 3' ends, but were not polyadenylated. They have acquired at their 5' end a heterologous 12- to 18-nucleotide-long sequence, which is not coded for by the virus. Sequencing of the 5' terminal region from single molecules cloned into pBR327 revealed that these primers are rich in C and G residues and possess a U or a C adjacent to the viral sequence.