Related Experiment Videos
Size distribution of rat liver nuclear RNA containing mRNA sequences
Abstract:
Total rat liver poly(A)-containing polysomal mRNA was size-fractionated on polyacrylamide gels in 98% formamide. Complementary DNA (cDNA) was prepared from the 8--14-S mRNA fraction and separated into sequences representing abundant and non-abundant mRNAs. The cDNA complementary to the abundant small mRNA of the rat liver cell (approximately 20 species) was hybridized to nuclear RNA of different lengths to determine the size distribution of nuclear RNA molecules which contain these messenger sequences. It was found that: 1. All abundant 8--14-S poly(A)-containing mRNAs have larger nuclear precursor molecules; 20% of the different messenger sequences are found in nuclear RNA of several times their cytoplasmic length. 2. 70% of the mass of the examined nuclear messenger sequences is in RNA molecules of a size similar to their polysomal mRNA; 30% are in larger than 18-S RNA and 2% are between 37 S and 44 S. 3. The majority of small messenger-containing RNA molecules in the RNA prepared from isolated nuclei are of true nuclear origin, since their frequency distribution differs significantly from that of the polysomal 8--14-S mRNA.
Insights
Rat liver cells process abundant messenger RNA (mRNA) precursors in the nucleus. These nuclear precursors are often larger than their final cytoplasmic mRNA forms, indicating nuclear processing steps.
Area of Science:
- Molecular Biology
- Cell Biology
- Genetics
Background:
- Polyadenylated mRNA plays a crucial role in protein synthesis.
- Understanding mRNA processing in the nucleus is key to gene expression regulation.
Purpose of the Study:
- To investigate the size distribution and origin of nuclear RNA molecules containing abundant rat liver messenger RNA sequences.
- To characterize the nuclear precursors of abundant 8-14S poly(A)-containing mRNAs.
Main Methods:
- Size fractionation of rat liver polysomal mRNA using polyacrylamide gel electrophoresis.
- Complementary DNA (cDNA) synthesis from mRNA fractions.
- Hybridization of cDNA to nuclear RNA of varying lengths.
Main Results:
- Abundant 8-14S poly(A)-containing mRNAs originate from larger nuclear precursor molecules.
- Messenger sequences are found in nuclear RNA molecules of diverse sizes, with a significant portion being larger than their cytoplasmic counterparts.
- The frequency distribution of nuclear messenger sequences differs from polysomal mRNA, suggesting true nuclear origin.
Conclusions:
- Rat liver nuclei contain precursor molecules for abundant mRNAs that are processed before export to the cytoplasm.
- Nuclear RNA processing involves size alterations, with some precursors significantly larger than mature mRNAs.
- The findings support a multi-step nuclear processing model for gene expression.