We have used a modification of the Berk-Sharp technique to determine that the 5' termini of the mouse 15 S beta-globin precursor and the mature mRNA have identical map coordinates. The modification involves the use of 5' (or 3') terminally labeled probes; it allows the detection of the precursor in the presence of excess mature mRNA.

A genomic clone that specifies a single polypeptide precursor for ricin, a toxic lectin of Ricinus communis (castor bean), was isolated, sequenced and Sl mapped. The gene encodes a 64 kDa precursor which contains, in the following order: a 24 or 35 amino acid signal peptide, the A chain, a 12 amino acid linker peptide, and the B chain. The 5'-end of the ricin mRNA maps approximately 35 bases upstream from the first methionine codon. Two putative TATA boxes and a possible CAAT box lie in the 5'-flanking region. Two possible polyadenylation signals were found in the 3' flanking region. No introns were found, which is typical of other lectin genes that have been sequenced. Southern blot analysis suggests that the castor bean genome contains approximately six ricin-like genes.

No abstract

Nuclear run-on assays carried out in the presence and absence of the RNA polymerase II inhibitor, ~t-amanitin, were used to determine the exact timing of the switch from inhibitor-sensitive transcription catalysed by host RNA polymerase II, to inhibitor-resistant transcription catalysed by the baculovirus-induced RNA polymerase. These studies revealed that the onset of ~-amanitin-resistant transcription is just after 6 h post-infection, simultaneous with the beginning of the late phase of infection. They also showed that transcripts from the p26 gene in the HindIII Q/P region and the p35 gene in the HindlII K/Q region of the viral genome are synthesized by the host RNA polymerase II both early and late in infection. On the other hand, transcripts of the p 10 gene in the HindII! Q/P region and the y transcripts in the HindIII K region are synthesized by the ~-amanitin-resistant, virus-induced RNA polymerase late in infection.

Autographa californica nuclear polyhedrosis virus-specific RNA synthesis in isolated nuclei of Spodoptera frugiperda cells in culture was monitored at different times postinfection. Up to 8 h postinfection viral RNA synthesis remained sensitive to 5 ,ug of a-amanitin per ml. During the course of infection this sensitivity decreased, and at 24 h postinfection RNA synthesis was completely resistant to a-amanitin. DEAE-Sephadex profiles of RNA polymerase isolated at 24 h postinfection showed a new, chromatographically distinct, a-amanitinresistant form whose kinetics and response to divalent cations differed from those of the host RNA polymerases. The possibility that this enzyme may be responsible for viral late transcription is discussed.