Abstract
Seryl-tRNA synthetase has been purified from the middle silk glands of Bombyx mori by successive chromatography on DEAE-Sephacel, hydroxylapatite, and Bio-Rex 70. The high abundance of seryl-tRNA synthetase in the middle silk glands may result from an adaptation of this organ for the production of the serine-rich protein, sericin. The enzyme is a dimer of Mr = 124,000 consisting of similar or identical subunits and has an oligomeric structure similar to its procaryotic and eucaryotic counterparts. Seryl-tRNA synthetase can be cleaved with trypsin to generate a fragment of Mr = 45,000 on sodium dodecyl sulfate gels; the presence of tRNASer protects the enzyme from tryptic cleavage. Conversion to the Mr = 45,000 species is accompanied by a 90% loss in aminoacyl-tRNA synthetase activity, but only a 20% loss in ATP PPi exchange activity.
Highlights
Seryl-tRNA synthetase has been purified from the synthetases that correspond to the most abundant amino middle silk glands of Bombyx mori by successivechro- acids in fibroin (10,ll)
The high abundance of seryl-tRNA syn- mori may be regulated in a manner similar to that of the thetase in the middle silk glands may result from an tRNAs, where the regulation is thought to occur primarily, if adaptationof this organ for the productionofthe not exclusively, at thelevel of transcription [12, 13]
The alanyl- and glycyl-tRNA synthetases were purified earlier in our laboratory from posterior silk glands [14] and we present here the purification of seryl-tRNA synthetase to homogeneity from the middle silk glands of B. mori
Summary
Seryl-tRNA synthetase has been purified from the synthetases that correspond to the most abundant amino middle silk glands of Bombyx mori by successivechro- acids in fibroin (10,ll). As a step toward understanding the regulation of aminoacyl-tRNA synthetases in B. mori, we have purified to hounits and has an oligomericstructuresimilarto its procaryotic and eucaryotic counterparts. Conversion to thMe, = 45,000species is accompanied by a90%loss in aminoacyl-tRNAs>nmogeneity three aminoacyl-tRNA synthetases corresponding to themost abundant amino acids in fibroin and sericin.
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