Question

Class I and Class II aminoacyl–tRNA synthetases differ in their

I. structural motifs.

II. anticodon recognition.

III. site of aminoacylation.

IV. amino acid specificity.

II, III

II, IV

II only

I, II, III, IV

I only

Answer 1

The correct option is I, II, III, IV.

Class I and Class II aminoacyl-tRNA synthetases differ in their structural motifs, anticodon recognition, site of aminoacylation and amino acid specificity.

Class I has two highly conserved sequence motifs. It aminoacylates at the 2'-OH of a terminal adenosine nucleotide on tRNA. It is usually monomeric or dimeric. Class II has three highly conserved sequence motifs. It aminoacylates at the 3'-OH of a terminal adenosine on tRNA and usually dimeric or tetrameric. Both classes of aminoacyl-tRNA synthetases are multidomain proteins. An aaRS consists of a catalytic domain and an anticodon binding domain in a typical scenario. Most of the aaRSs of a given specificity are evolutionarily closer to each another than to aaRSs of another specificity. Most of the aaRSs of a given specificity also belong to a single class.