Isozymes of ribonuclease and the changes in their relative levels during development in the cellular slime mould Dictyostelium discoideum

Abstract

The isozymes of ribonuclease were analyzed in cell-free, crude extracts of Dictyostelium discoideum by activity staining of polyacrylamide gels after electrophoresis. The relative levels of three isozymes were then examined during the growth and during the first stages of multicellular development. We observed the replacement of two of these three isozymes by two other isozymes at the pseudoplasmodial stage. These isozymes were different from ribonuclease T1 in terms of their mobility in polyacrylamide gels during electrophoresis. The mobilities of two of the isozymes, DdI and DdII, were 59 and 42% of that of ribonuclease T1. The changes in the relative levels of the isozymes during development are discussed.

Unusual Occurrence of Two Bona-Fide CCA-Adding Enzymes in Dictyostelium discoideum

“…In the inverse expression profiles of CCA1 and CCA2 during the life cycle of D. discoideum , mRNA levels of Q/N-rich CCA2 are upregulated during cell aggregation ( Figure 3 B), indicating that this enzyme has a specific function at this developmental stage. Based on dictyExpress data, such differentiation correlated with changes in gene expression profiles are also observed for several RNases [ 41 ] and enzymes involved in tRNA modification (methyltransferase) [ 69 ].…”

“…Furthermore, the differential expression of isoenzyme forms is also described for a large number of D. discoideum proteins with possible regulatory potential such as ribonuclease [ 41 ], protein kinases [ 40 ], protein tyrosine phosphatase PTP3 [ 43 ], DNA helicase [ 70 ], chromatin remodeler CHD [ 71 ] and tRNA His guanylyltransferases (Thg1) [ 72 ] in D. discoideum . For most of these isozymes, different functions and substrates could be identified.…”

“…Surprisingly, gene expression data reveal an inverse expression of the corresponding cca1 and cca2 genes during the individual developmental stages. This might hint at the participation of both CCA-adding activities in the fine-tuning of the complex developmental cycle, as was shown for a remarkable number of other isoenzymes in D. discoideum [37][38][39][40][41][42][43].…”

Intracellular ribonuclease isozyme activity of the cellular slime mold cells,Dictyostelium discoideum Ax2 andDictyostelium mucoroides

“…We previously reported the isozymes of the ribonuclease in D. discoideum NC4 cells and the changes in their relative levels during development (UCHIYAMA et al 1991), using a reversed activity staining technique for ribonucleolytic activity in polyacrylamide gels after electrophoresis (electrophoretic zymogram) which provides a very convenient and sensitive method for the detection of isozymes in crude extracts (WILSON 1971, TAKAIWA and TANIFUJI 1978, UCHIYAMA et al 1992, YASUDA et al 1992. The changes in the relative levels of the isozymes during development may reflect the changes in the substrates of the enzymes; the enzymes may predominantly hydrolyze bacterial RNAs in the growth phase, however, it may only hydrolyze cellular RNAs during the development phase which is introduced by deprivation of bacteria.…”