Differential phosphate labeling of stress protein polypeptides in toxic dose response during S-phase of mouse lymphoma cells: a micro-electrophoretic study

Abstract

Following dosing with various levels of sodium arsenite (NaAsO2), differential [32P]-incorporation (turnover) of polypeptide fragments, generated by protease V8, from a set of four closely related stress proteins (SPs), termed 'c','b','x' and 'y', (80,000-84,000 Mr) was investigated by polyacrylamide gel (PAG) autoradiography. These SPs were physically sorted sequentially from five partitions of S-phase of a mouse lymphoma cell line (YAC-1). The fragments of each of the four SPs exhibited differential [32P]-incorporation patterns with progression in S-phase following varied dose levels of NaAsO2. The majority of V8 protease-fragments of the four SPs had identical electrophoretic mobilities. A minority of polypeptides showed varied distribution among the four SPs and these fragments revealed increased [32P]-labeling progressively in S-phase. These fragments were the most sensitive to altered dose levels of NaAsO2. It was suggested that these four SPs are discrete but structurally similar proteins. A group of other SPs (S1, S2 and S3) observed predominantly in S-phase, showed reduction in polypeptide labeling during S with varied dosing of NaAsO2. The [32P]-labeling of fragments from the SPs seems generally to follow an ordered scheme of turnover (phosphorylation-dephosphorylation) during S-phase.