[' ', ' ', 'B.', 'Progress', 'Report.', 'Phenobarbital', 'Induction', 'in', 'Contrast', 'to', '3MC:', 'Both', 'phenobarbital', '(PB)', 'and', '3MC', 'are', 'potent', 'inducers', 'of', 'cytochrome', 'P450,', 'with', 'the', 'former', 'resulting', 'in', 'increases', 'in', 'liver', 'P450b', 'and', 'P450e,', 'while', 'after', 'pretreatment', 'with', 'the', 'latter,', 'increases', 'in', 'cytochromes', 'P450c', 'and', 'P450d', 'are', 'observed.', 'In', 'this', 'study,', 'we', 'were', 'interested', 'in', 'comparing', 'the', 'sizes', 'of', 'the', 'messenger', 'RNAs', 'for', 'cytochrome', 'P&50b', 'and', 'P450c', 'by', 'using', 'Northern', 'blot', 'hybridization', 'analysis', 'of', 'Poly(A’)', 'RNA', 'fractions', 'prepared', 'from', 'the,', 'livers', 'of', 'rats', 'that', 'had', 'been', 'treated', 'both', 'either', 'PB', 'or', '3MC.', 'The', 'Poly(A‘)', 'RNA', 'fractions', 'were', 'prepared', 'from', 'liver,', 'were', 'electrophoresed', 'on', 'agarose', 'gels', 'under', 'denaturing', 'formaldehyde', 'conditions', '(to', 'disrupt', 'any', 'secondary', 'structure},', 'were', 'transferred', 'to', 'nitrocellulose', 'by', 'the', 'Northern', 'technique', 'and', 'the', 'nitrocellulose.', 'was', 'then', 'hybridized', 'with', 'either', 'nick-translated', '(radioactive)', 'pEB339', '(recombinant', 'DNA', 'probe', 'for', 'mRNA', '850)', 'or', 'pPHs', '(recombinant', 'DNA', 'probe', 'for', 'mMRNAp', 'ys', '4', ').', 'The', 'constructiby', 'of', 'pEB339', 'was', 'discussed', 'in', 'earlier', 'progress', 'reports', 'Wile', 'pPH8', 'is', 'treated', 'In', 'a', 'later', 'section', 'of', 'this', 'progress', 'report', '(actually', 'publication', '#3}.', 'We', 'found', 'that', 'the', 'mRNA', '50¢', 'Was', 'Of', '3.7', 'Kb', '(when', 'compared', 'with', 'DNA', 'standards,', 'this', 'value', 'was', 'corracted', 'down', 'to', 'approximately', '3.3', 'Kb)', 'in', 'length.', 'One', 'would', 'predict', 'from', 'the', 'molecular', 'weight', 'of', 'cytochrome', 'P450c', 'that', 'a', 'mRNA', 'of', 'approximately', '1.5', 'Kb', 'would', 'be', 'in', 'order.', 'Consequently,', 'the', 'mature', 'mRNAGy', 'é', 'contains', 'more', 'than', 'twice', 'the', 'information', 'needed', 'for', 'its', 'function', 'with', '508', 'of', 'the', 'molecule', 'non-coding', 'In', 'nature.', 'A', 'similar', 'picture', 'was', 'found', 'when', 'mRNA,', 'oh', '“4S', 'sized', 'under', 'these', 'conditions', 'with', 'the', 'appropriate', 'radioactively”', 'fassled', 'probe.', 'In', 'this', 'case,', 'mRNA', '50h,', 'Was', '4.0', 'Kb', 'in', 'size.', 'We', 'also', 'successfully', 'translated', 'the', 'RNA', 'present', 'in', 'the', '4.0', 'Kb', 'region', 'of', 'an', 'agarose', 'get', 'electrophoretogram', 'in', 'an', 'in', 'vitro', 'rabbit', 'reticulocyte', 'system.', 'The', 'translated', 'products', 'were', 'immunoprecipitated', 'with', 'authentic', 'monospecific', 'antibody', 'to', 'cytochrome', 'P450b.', 'The', '4.0', 'Kb', 'RNA', 'was', 'also', 'removed', 'after', 'electrophoresis', 'of', 'control', 'Poly(A)', 'RNA', 'and', 'the', 'level', 'of', 'induction', 'of', 'mRNA', 'was', 'determined.', 'The', 'transcription', 'of', 'this', 'mRNA', 'was', 'increased', 'by', 'approximately', '15~fold', 'by', '15', 'hr', 'after', 'pretreatment', 'of', 'the', 'rats', 'with', 'PB.', 'These', 'studies', 'have', 'been', 'Published', 'and', 'appear', 'as', 'Publication', '#1.', 'Copies', 'of', 'the', 'publication', 'are', 'provided', 'with', 'this', 'Progress', 'Report.', 'Regulation', 'of', 'Expression', 'of', 'Cytochrome', 'P~450:', 'The', 'levels', 'of', 'mRNA', 'Paso', 'OF', 'in', 'fact', 'any', 'mRNA', 'that', 'is', 'present', 'in', 'the', 'cytoplasm', 'reflect', 'not', 'only', 'Re', 'rate', 'of', 'transcription', 'and', 'the', 'half-life', 'of', 'the', 'mRNA,', 'but', 'also', 'the', 'extent', 'of', 'post-transcriptional', 'events,', 'i.e.,', 'polyadenylation,', '"capping",', 'splicing', 'and', 'transport', 'from', 'the', 'nucleus', 'into', 'the', 'cytoplasm.', 'We', 'have', 'examined', 'the', 'events', 'of', 'nuclear', 'processing', 'of', 'mRNA', 'precursors', 'in', 'the', 'liver', 'from', 'either', '3MC-', 'or', 'PB-pretreated', 'rats.', 'As', 'early', 'as', '1', 'hr', 'after', 'pretreatment', 'with', 'PB,', '6.3', 'and', '4.8', 'Kb', 'nuclear', 'precursor', 'mRNA,', 'db', 'Were', 'observed', 'as', 'well', 'as', 'the', 'mature', 'MRNA', 'ycope', 'which', 'was', '3.8-4%.0', 'KB', 'In', 'size.', 'The', 'level', 'of', 'mature', 'mRNA', '4506', 'reached', 'a', 'maximum', 'in', 'the', 'cytosol', '(associated', 'with', 'polyribosomes)', '305-20', 'hr', 'while', 'nuclear', 'precursors', 'were', 'at', 'their', 'highest', 'levels', 'at', 'about', '2-4', 'hr.', 'These', 'data', 'suggest', 'that', 'transport', 'from', 'the', 'nucleus', 'to', 'the', 'cytoplasm', 'may', 'be', 'partially', 'rate-', 'limiting', 'in', 'determining', 'the', 'level', 'of', 'cytosolic', 'MRNAprr', 'oy:', ' ', '50147519']