Transcription of intracisternal A-particle genes in mouse myeloma and Ltk- cells.

In vivo- and in vitro-synthesized RNA from the murine plasmacytoma MOPC-315 was found to hybridize to all regions of a 7.2-kilobase-pair intracisternal A-particle (IAP) gene. IAP-specific transcripts were also detected in mouse Ltk- cells, but not in cells derived from normal tissues (kidney, liver, spleen) of 6-week-old BALB/c mice. Three RNA species of 7.2, 5.3, and 3.8 kilobases were identified by Northern blot analysis of MOPC-315 polyadenylated RNA. The 7.2- and 5.3-kilobase transcripts were found in greater levels in nuclear as compared with whole cell RNA, suggesting the involvement of one or more of the following mechanisms: RNA processing, preferential nuclear transport, or differential RNA stability. We show that the primary IAP transcript is initiated within the long terminal repeat by hybridization analysis with restriction digests of cloned IAP DNA and [gamma-S]pppApNp ... RNA synthesized in nuclei with [gamma-S]ATP as the RNA initiating probe. Low concentrations of alpha-amanitin (2 micrograms/ml) inhibited IAP RNA synthesis by greater than 90%, suggesting that RNA polymerase II is responsible for IAP transcription.