Genomic organization of rat rDNA

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Ribosomal DNA (rDNA) encodes ribosomal RNA (rRNA), essential for protein synthesis.
• Understanding rDNA structure and variations is crucial for studying gene regulation and evolution.
• Previous studies have characterized rDNA in various species, but detailed mapping in specific rat strains was needed.

Purpose of the Study:

• To generate a detailed restriction map of a 10.9 KB region of rat rDNA.
• To identify and characterize polymorphisms in the rDNA of Sprague-Dawley and BD-9 rats.
• To investigate repetitive DNA sequences upstream of the rRNA gene initiation site.

Main Methods:

• Restriction mapping of cloned rat rDNA and total rat DNA.
• Comparison of restriction patterns between different rat strains.
• Analysis of DNA sequences, including tandem repeats and repetitive elements.

Main Results:

• Identical rDNA restriction patterns were observed between Sprague-Dawley and BD-9 rats, and with cloned rDNA.
• A major polymorphism was identified: a 0.9 KB insertion in the non-transcribed spacer region upstream of the 45S pre-rRNA initiation site.
• This insertion region contains tandem repeats (approx. 130 bp) with poly-T tracts, similar to mouse rDNA elements.
• Highly repetitive DNA sequences were located at 2.8 KB and 4.3 KB upstream, with the 2.8 KB sequence annealing to a rat growth hormone gene-derived Alu-equivalent.

Conclusions:

• Rat rDNA sequences are highly conserved between Sprague-Dawley and BD-9 strains.
• A significant, strain-specific polymorphism exists in the non-transcribed spacer of rDNA.
• The identified repetitive elements may play roles in rDNA regulation or evolution.