3-Methylpseudouridine as a fermentation product.

3-Methylpseudouridine (beta isomer) has been identified in fermentation broths of Nocardia lactamdurans. It accumulates at quite high levels following the accumulation of extracellular uracil in strains exhibiting increased levels of de novo pyrimidine biosynthetic enzymes. It is labeled by exogenous uracil, and appears to result from an irreversible modification of one of the components of the elevated pyrimidine pool. Its methyl group is labeled efficiently by [methyl-14C]methionine.