Insertion of Mu into the Shrunken 1 gene of maize affects transcriptional and post-transcriptional regulation of Sh1 RNA.

Insertion of a Mu transposable element at the Shrunken 1 (Sh1) locus of maize has resulted in kernels with the typical collapsed appearance of sh mutants. Molecular analysis of the mutant gene has revealed the presence of a 1.4 kb insertion immediately upstream from the normal transcriptional start site. Mu insertion has brought about a series of changes in gene expression: the mRNA cap site has been shifted downstream so that it now lies inside the Mu element; transcription is reduced approximately sixfold, and the sh mRNA steady-state level is less than 4% of that found in the nonmutant. This disparity reflects a mutational defect in post-transcriptional regulation which is manifested as a decrease in Sh RNA abundance.