A second cytosolic ascorbate peroxidase (cAPX; EC 1.11.1.11) gene fromArabidopsis thalianahas been characterised. This second gene (designatedAPX1b) maps to linkage group 3 and potentially encodes a cAPX as closely related to that from other dicotyledonous species as to the other member of this gene family (Kubo et al, 1993, FEBS Lett 315: 313–317; here designatedAPX1a), which maps to linkage group 1. In contrast, the lack of sequence similarity in non-coding regions of the genes implies that they are differentially regulated. Under non-stressed conditions onlyAPX1ais expressed.APX1bwas identified during low-stringency probing using a cDNA coding for pea cAPX which, in turn, was recovered from a cDNA library by immunoscreening with an antiserum raised against tea plastidial APX (pAPX). No pAPX cDNAs were recovered, despite the antiserum displaying specificity for pAPX in Western blot
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