Repeated sequences in L-cell mRNA complementary to long deoxypolypyrimidines

Area of Science:

• Molecular Biology
• Genetics
• Eukaryotic Gene Expression

Background:

• Long pyrimidine tracts are highly conserved, repeated DNA sequences in eukaryotic genomes.
• These sequences are known to be transcribed into RNA in L-cells.

Purpose of the Study:

• To investigate the association of pyrimidine tracts with specific RNA fractions in L-cells.
• To determine the prevalence and characteristics of sequences complementary to deoxypolypyrimidines in mRNA.

Main Methods:

• Saturation hybridization experiments using fractionated cellular RNA.
• Enzymatic removal of poly(A+) tracts from mRNA.
• Gel electrophoresis of RNAase-resistant hybrids to measure polypurine region size.

Main Results:

• Polypyrimidines preferentially hybridize with polysomal poly(A+) RNA and nuclear poly(A+) RNA.
• Hybridization is unaffected by the removal of poly(A+) tracts from mRNA.
• Approximately 1% of mRNA contains regions complementary to deoxypolypyrimidines, with an average polypurine region size of 35 nucleotides.
• About half of poly(A-) mRNA molecules in L-cells contain sequences complementary to deoxypolypyrimidines.

Conclusions:

• Transcribed pyrimidine tracts are present in various mRNA fractions, including poly(A-) mRNA.
• The conservation and transcription of these sequences suggest a crucial, though currently unknown, function in eukaryotic gene expression.