Effects of pancreozymin, urecholine and actinomycin D on the metabolism of ribonucleic acid by canine pancreas.
1. Canine pancreas slices were incubated with [6-(14)C]orotic acid and the rate of its incorporation into RNA was measured. RNA was fractionated by shaking homogenates with phenol at 2 degrees , 50 degrees , 65 degrees and 80 degrees . Cytoplasmic RNA was extracted at the lowest temperature and nuclear RNA at the higher temperatures. The samples were centrifuged through sucrose gradients and the E(260) and (14)C-sedimentation patterns determined. Incorporation of orotic acid was very rapid into cytoplasmic 4s RNA. This probably represents end-group turnover. No incorporation into cytoplasmic ribosomal RNA was observed. 2. The nuclear 50 degrees -RNA exhibited two E(260) peaks, at 18s and 28s. This portion of the sample contained but moderate amounts of [(14)C]RNA. The highly labelled material had sedimentation coefficients in the range 35-50s. The nuclear 65 degrees -RNA showed an E(260) peak at 16s. The [(14)C]RNA peak occurred at 25-35s and this portion demonstrated the highest specific activity of any RNA fraction. 3. The 50 degrees -RNA, 65 degrees -RNA and 80 degrees -RNA were hydrolysed and their base compositions were determined. All three samples possess a ribosomal type of composition (G+C)/(A+U)=(1.4-1.7). For this reason they are considered to contain ribosomal precursor RNA as their major constituent. 4. Actinomycin D (0.5mug./ml.) in the incubation medium inhibited incorporation of orotic acid into both nuclear fractions but not into 4s RNA. 5. The cholinergic drug Urecholine inhibited incorporation into the heavy, high-specific-activity portions of the nuclear fractions but did not inhibit incorporation into the ribosomal precursor type of nuclear RNA. A similar result was also obtained with the hormone pancreozymin. Moderate inhibition of incorporation of orotic acid into 4s RNA likewise resulted from the presence of the drug and the hormone.
D000818:Animals; D002247:Carbon Isotopes; D002467:Cell Nucleus / Q000032:analysis; D002499:Centrifugation, Density Gradient; D002766:Cholecystokinin / Q000494:pharmacology*; D002794:Choline / Q000494:pharmacology*; D003593:Cytoplasm / Q000032:analysis; D003609:Dactinomycin / Q000494:pharmacology*; D004285:Dogs; D010179:Pancreas / Q000378:metabolism*; D012313:RNA / Q000032:analysis / Q000378:metabolism*
D002247:Carbon Isotopes; D003609:Dactinomycin; D012313:RNA; D002766:Cholecystokinin; D002794:Choline