Abstract
Defective Kirsten murine sarcoma virus was present as leukemia virus pseudotype [Ki-MSV(MLV)] in a 10- to 100-fold excess over its helper, Kirsten murine leukemia virus (Ki-MLV), when the two viruses were propagated in an NRK rat cell line. The s(omega,20) of the fastsedimenting RNA complex of Ki-MLV and of Ki-MSV-(MLV) was 62 S and 55 S, respectively. Gel electrophoresis in buffered aqueous or formamide solution of the dissociated 62S RNA complex of Ki-MLV showed a single major peak of molecular weight about 2.5 x 10(6). Dissociated 55S RNA of Ki-MSV(MLV) was resolved into a major component with a higher electrophoretic mobility than that of Ki-MLV RNA and molecular weight about 2.3 x 10(6). Occasionally, a minor component with the same electrophoretic mobility as Ki-MLV RNA was observed in Ki-MSV(MLV) RNA; it is thought to be the RNA of Ki-MLV present as helper virus in our stocks of Ki-MSV(MLV). The RNA of an endogenous rat C-type RNA virus was electrophoretically different from both Ki-MLV RNA and Ki-MSV(MLV) RNAs. Oligonucleotide fingerprinting of the RNAs digested with RNase T1 indicated that the RNAs of Ki-MSV(MLV) and Ki-MLV are different. However, the extent of the difference between the two RNAs could not be estimated by this method. The heat-dissociated 50-70S RNAs of two other defective murine sarcoma-leukemia viruses; Harvey-MSV(MLV) and Moloney-MSV(MLV) and of defective spleen-focus-forming Friend virus were resolved electrophoretically into two components. The larger components had the same electrophoretic mobility as the RNA of Ki-MLV or Moloney MLV. The smaller were not present in leukemia virus. It is suggested that the small RNA components of the two murine viruses and of Friend virus represent specific genetic information of these replication-defective transforming viruses. Possible relationships between the RNAs of murine leukemia viruses and replication-defective murine sarcoma and Friend viruses are discussed.