Figure 9.
Tentative model depicting the possible mRNA production regulation by gene looping at the GAT1 locus. (A). In rich nitrogen conditions, wild type cells produce a wide variety of mRNAs differing in their 5′ and 3′ ends, but the major species is a full length RNA (FL GAT1) spanning from the 2nd in phase ATGMet codon (ATGM40) to the 1st Stop codon. (B). In nitrogen derepressing conditions, the production of the full length GAT1 mRNA is unchanged, although DNA-bound GATA factors activate the expression from the GAT1 promoter. Premature transcription termination occurs to generate the most abundant mRNA species, SH GAT1, and the transcription machinery is recycled at the GAT1 promoter, as indicated by the dotted arrow. (C). In proline-grown GAT1Δ60 cells, no termination and no recycling occurs, resulting in the absence of SH GAT1. FL GAT1 production remains unchanged.