A test of Chargaff's second rule.

Area of Science:

• Genomics
• Molecular Biology
• Bioinformatics

Background:

• The Chargaff parity rule, stating A=T and C=G in single-stranded DNA, was established in 1968.
• This rule has been widely confirmed in bacterial and eukaryotic double-stranded DNA genomes.
• Previous studies have not tested this rule in single-stranded DNA or RNA genomes.

Purpose of the Study:

• To investigate the validity of the Chargaff parity rule across diverse genome types, including single-stranded DNA and RNA.
• To analyze over 3400 genomic sequences encompassing double-stranded DNA, single-stranded DNA, and RNA genomes.
• To determine the implications of the parity rule's adherence or failure on genome evolution and codon usage.

Main Methods:

• Bioinformatic analysis of over 3400 publicly available genomic sequences.
• Categorization of genomes into double-stranded DNA, single-stranded DNA, and RNA (both strandedness).
• Statistical examination of nucleotide base frequencies (Adenine, Thymine, Guanine, Cytosine) within each genome category.

Main Results:

• The Chargaff parity rule (A=T, C=G) was confirmed in most double-stranded DNA genomes, excluding organellar DNA.
• The parity rule was found to fail in single-stranded DNA genomes and all RNA genomes.
• Significant correlations were observed between the adherence to the parity rule and patterns of genome evolution and codon selection.

Conclusions:

• The Chargaff parity rule is a fundamental characteristic of most double-stranded DNA genomes but not single-stranded or RNA genomes.
• The findings suggest the parity rule acts as a selective pressure influencing genome evolution and codon usage strategies.
• This study expands the understanding of nucleotide composition rules across different nucleic acid types and their evolutionary significance.