Human 60 kDa SS-A/Ro ribonucleoproteins (RNPs) are composed of one of the four small Y RNAs and at least two proteins, Ro60 and La.

The La protein is a 47 kDa polypeptide that frequently acts as an autoantigen in systemic lupus erythematosus and Sjögren syndrome.

[2] In the nucleus, La binds to the 3'UTR of nascent RNAP III transcripts to assist in folding and maturation.

[3] In the cytoplasm, La recognises specific classes of mRNAs that contain a 5'-terminal oligopyrimidine (5'TOP) motif known to control protein synthesis.

[5] Homologous La domain-containing proteins have been identified in a wide range of organisms except Archaea, bacteria and viruses.