Abstract
BackgoundThe RPS4 gene codifies for ribosomal protein S4, a very well-conserved protein present in all kingdoms. In primates, RPS4 is codified by two functional genes located on both sex chromosomes: the RPS4X and RPS4Y genes. In humans, RPS4Y is duplicated and the Y chromosome therefore carries a third functional paralog: RPS4Y2, which presents a testis-specific expression pattern.ResultsDNA sequence analysis of the intronic and cDNA regions of RPS4Y genes from species covering the entire primate phylogeny showed that the duplication event leading to the second Y-linked copy occurred after the divergence of New World monkeys, about 35 million years ago. Maximum likelihood analyses of the synonymous and non-synonymous substitutions revealed that positive selection was acting on RPS4Y2 gene in the human lineage, which represents the first evidence of positive selection on a ribosomal protein gene. Putative positive amino acid replacements affected the three domains of the protein: one of these changes is located in the KOW protein domain and affects the unique invariable position of this motif, and might thus have a dramatic effect on the protein function.ConclusionHere, we shed new light on the evolutionary history of RPS4Y gene family, especially on that of RPS4Y2. The results point that the RPS4Y1 gene might be maintained to compensate gene dosage between sexes, while RPS4Y2 might have acquired a new function, at least in the lineage leading to humans.
Highlights
RPS4 genes encode for the ribosomal protein small subunit 4 (29kD; 263 amino acids), a protein involved in mRNA binding and located at the 40S/60S subunit interface of the small ribosomal subunit [1]
Maximum likelihood analyses of the synonymous and non-synonymous substitutions revealed that positive selection was acting on RPS4Y2 gene in the human lineage, which represents the first evidence of positive selection on a ribosomal protein gene
The results point that the RPS4Y1 gene might be maintained to compensate gene dosage between sexes, while RPS4Y2 might have acquired a new function, at least in the lineage leading to humans
Summary
RPS4 genes encode for the ribosomal protein small subunit 4 (29kD; 263 amino acids), a protein involved in mRNA binding and located at the 40S/60S subunit interface of the small ribosomal subunit [1]. Jegalian and Page [5] found a Y-linked copy in a marsupial species, the gray short-tailed opossum (Monodelphis domestica), and Skaletsky et al [6] found this gene in the first X-degenerate block suggesting that RPS4Y1 was present before mammalian radiation. Another Y-linked copy has been discovered on the human Y chromosome and has been named RPS4Y2 [6] in order to distinguish it from the first copy, which is called RPS4Y1. These authors showed that the expression of ribosomal protein genes must be regulated in a coordinated way in order to ensure the correct assembly of the elements of the ribosomal complex
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