DOES GENE PALB REGULATE THE TRANSCRIPTION OR THE POST TRANSLATIONAL MODIFICATION OF PI-REPRESSIBLE PHOSPHATASES OF ASPERGILLUS-NIDULANS

When grown on low-Pi medium, the chaA1 pabaA1 palB7 mutant of Aspergil lus nidulans excretes an acid phosphatase with steady-state kinetic pr operties, temperature sensitivity and electrophoretic mobility differe nt from those of the enzyme excreted by the pabaA1 strain. The enzyme excreted by the pabaA1 strain at pH 6.5 showed PNP-P activity with neg ative cooperativity (K-0.5 = 0.87 +/- 0.06 mM, n = 0.68 +/- 0.03) wher eas the enzyme excreted by the chaA1 pabaA1 palB7 mutant showed Michae lian kinetics (K-m = 0.46 +/- 0.03 mM, n = 1.00 +/- 0.02). The apparen t half-lives at 60 degrees C, pH 5.5, of acid phosphatase excreted by the pabaA1 and chaA1 pabaA1 palB7 strains were 58.6 +/- 4.9 min and 21 .5 +/- 1.8 min, respectively. Furthermore, the electrophoretic mobilit y of acid phosphatases excreted by the palA1, palB7, palC4, palE11 and palF15 mutants of A. nidulans was altered and differed from the elect rophoretic mobility of the enzyme excreted by the wildtype strain. Als o, the palB7 mutation altered the electrophoretic pattern of acid phos phatases synthesized on high-Pi medium. These results are compatible w ith the post-translational modifications in the Pi-repressible phospha tases rather than with the action of gene palB in controlling the tran scription of structural genes of these enzymes.