The characterization of phosphoseryl tRNA from lactating bovine mammary gland

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Abstract
BD-cellulose and RPC-5 chromatography of tRNA iso lated from lactating bovine mammary gland showed the presence of four seryl-tRNA isoacceptors. The species, tRNA with the strongest affinity for BD-cellulose (required ethanol in the elution buffer) could be phosphorylated in the presence of serine, [γ-32P]-ATP, seryl-tRNA synthetase and phosphotransferase activity from the same tissue. O-Phosphoserine was identified as the 32P-labbled product after mild alkaline hydrolysis of this aminoacylated tRNA. Pancreatic ribonuclease treatment of the aminoacylated tRNA yielded a labelled product which was identified as phosphoseryladenosine. These results indicated there is a specific phosphoseryl tRNA species in lactating bovine mammary gland. It appears that the formation of phosphoseryl-tRNA proceeds by enzymic phosphorylation of seryl-tRNA.