THE INITIAL ASSOCIATION OF A TRUNCATED FORM OF THE NEUROSPORA PLASMA-MEMBRANE H-ATPASE AND OF THE PRECURSOR OF YEAST INVERTASE WITH MICROSOMES ARE DISTINCT PROCESSES()

Translocation and integration activities were assessed in Neurospora m icrosomes (nRM) after modification either by a sulfhydryl alkylating r eagent or by a proteinase. A Neurospora in vitro system was programmed with RNA transcripts that encode the amino-terminal 194 amino-acid re sidues of the Neurospora plasma membrane H+-ATPase (pma194+) or the 26 2 amino-acid residues of the precursor of yeast invertase (preinv262). The processing of preinv262 was blocked in N-phenylmaleimide- and in trypsin-pretreated nRM. In contrast, the binding of preinv262 to micro somes was unaffected in the chemically alkylated nRM, but was affected in the trypsin-pretreated nRM. In the chemically alkylated vesicles, the integration of the pma194+ was not affected, but was partially blo cked in the trypsin-pretreated vesicles. These data imply that trypsin -sensitive components are required for these activities in nRM, and th at binding, translocation and integration can be differentiated by the ir sensitivity to chemical alkylation of sulfhydryl groups in nRM. Eva luated also were the effects of temperature on translocation and integ ration activities in the nRM. These were maximal at 20-degrees-C, wher eas the binding of preinV262 was maximal at 0-degrees-C. Taken togethe r, these data demonstrate that the processing of preinv262 by nRM can be resolved into two steps: binding of the precursor protein to nRM an d subsequent translocation into the lumen of the vesicles. Whereas, th e integration of the pma194+ into nRM could not be resolved into separ able steps. Taken together, these results are interpreted to imply tha t the initial association of truncated forms of the pma+ and the precu rsor of invertase to the surface of the nRM are distinct processes.