Question

How many aaRSs and classes are there in a cell? Are they all related evolutionarily?  

Answer 1

An aminoacyl-tRNA synthetase (aaRS or ARS) or tRNA -ligase is an enzyme which attaches an amino acid onto its tRNA.

As there are 20 different amino acids , there are 20 different aaRSs.

2 classes ; each has 10 enzymes

Class 1; has TWO higly conserved sequence motifs. They are monomeric or dimeric.

Class 2 ; has THREE motifs and are dimeric or tetrameric.

aaRS of a given specifity (or class) are evolutionarily closer to each other than to that of another specificity.

aaRSs paralogs within the same species shows a high degree of divergence between them.

AlaRS, GlyRS, LeuRS, IleRS and ValRS are the most evolutionarily stable aaRSs. GluRS, LysRS, and CysRS have paralogs.

With the exception of AlaRS , other 19 aaRSs in the humans have at least one new domain or motifs.