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Evolution of nucleic acids coding for ribonucleases: the mRNA sequence of mouse pancreatic ribonuclease
C Schüller1, H M Nijssen, R Kok
1Biochemisch Laboratorium, Rijksuniversiteit Groningen, The Netherlands.
Abstract:
The cDNA of mouse pancreatic mRNA has been cloned. After the library was screened with a rat ribonuclease cDNA probe, the positive clones were isolated and sequenced. There were no differences from the previously determined protein sequence. The mRNA codes for a preribonuclease of 149 amino acid residues including a signal peptide of 25 amino acids. The 3' noncoding region has a length of 260 bp, and the total mRNA length is approximately 940 bp. Comparison with the rat pancreatic ribonuclease sequence showed a high rate of nucleotide substitution. Within the coding region, nonsynonymous and synonymous substitution rates are 4.3 X 10(-9) and 15 X 10(-9) nucleotide substitutions/site/year, respectively. The latter value is one of the highest rates observed in the molecular evolution of mammalian nuclear genes. In the signal sequences the synonymous substitution rate is much lower and about the same as the nonsynonymous rate. Signal sequences of other mouse and rat proteins also exhibit little difference between synonymous and nonsynonymous rates. The sequences of rat and mouse pancreatic ribonuclease messengers were compared with those of bovine pancreatic, seminal, and brain ribonuclease. While the 3' noncoding regions of rat and mouse are very similar, as are those of the three bovine messengers, there is no significant similarity between both rodent and the three bovine messengers for the greater part of these regions. There is a duplication of approximately 50 nucleotides in the 3' noncoding region of the bovine messengers, with a region rich in A and C in between. The presence of this structural feature may be correlated with recent gene duplications that have occurred in the bovine genome.
Insights
Mouse pancreatic messenger RNA (mRNA) was cloned and sequenced, revealing a preribonuclease. High nucleotide substitution rates were observed, particularly in coding regions, suggesting rapid molecular evolution in mammalian nuclear genes.
Area of Science:
- Molecular Biology
- Evolutionary Genetics
Background:
- Cloning and sequencing of mouse pancreatic messenger RNA (mRNA).
- Utilizing a rat ribonuclease cDNA probe for library screening.
Purpose of the Study:
- To characterize the mouse pancreatic ribonuclease mRNA sequence.
- To investigate evolutionary rates and sequence divergence among mammalian ribonucleases.
Main Methods:
- Complementary DNA (cDNA) cloning and sequencing.
- Sequence comparison between mouse, rat, and bovine ribonuclease genes.
- Analysis of nucleotide substitution rates (nonsynonymous and synonymous).
Main Results:
- Mouse pancreatic mRNA codes for a preribonuclease (149 amino acids) with a 25-amino acid signal peptide.
- High synonymous nucleotide substitution rates (15 x 10^-9/site/year) in coding regions, indicative of rapid molecular evolution.
- Significant sequence divergence between rodent and bovine ribonuclease 3' noncoding regions, with structural differences in bovine sequences possibly linked to gene duplication.
Conclusions:
- Mouse pancreatic ribonuclease mRNA sequence is conserved at the protein level but shows high evolutionary rates at the nucleotide level.
- Distinct evolutionary patterns observed in coding versus signal sequences.
- Comparative analysis reveals significant divergence and structural variations in noncoding regions of mammalian ribonucleases, potentially reflecting genome evolution.