Ornithine decarboxylase inThermus thermophilus: An RNA-associated enzyme

Summary Ornithine decarboxylase (ODC) ofThermus thermophilus is associated with the nucleoid protein fraction. Analysis of this fraction by agarose gel electrophoresis and immunostaining revealed that ODC was bound to two groups of RNA-protein complexes. These two complexes of 1.5 and 0.6 kb in size disappeared from the gel by RNase A treatment or migrated to small molecular weight complexes by proteinase K treatment. Phenol extraction of either the nucleoid fraction or the eluted RNA-protein complexes from the agarose gel, shows that both contain the 0.56kb RNA. Both RNA-protein complexes contain the ODC protein (55 kDa) but their protein composition differs in at least six proteins. Extraction of the nucleoid fraction with H₂SO₄, indicates that ODC was present in the acid-soluble fraction, showing that it is a non-histone protein tightly bound to 0.56kb RNA. The purified ODC by various columns (140-fold), is close to homogeneity and still carries the 0.56kb RNA further explaining all the difficulties in the purification of this enzyme.