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Transcription of rRNAs in Escherichia coli is directed from seven redundant rRNA operons, which are mainly regulated by their P1 promoters. Here we demonstrate by in vivo measurements that the amounts of individual rRNAs transcribed from the different operons under normal growth vary noticeably although the structures of all the P1 promoters are very similar. Moreover, we show that starvation for amino acids does not affect the seven P1 promoters in the same way. Notably, reduction of transcription from rrnD P1 was significantly lower compared to the other P1 promoters. The presence of DksA was shown to be crucial for the ppGpp-dependent downregulation of all P1 promoters. Because rrnD P1 is the only rrn promoter starting with GTP instead of ATP, we performed studies with a mutant rrnD promoter, where the initiating G+1 is replaced by A+1. These analyses demonstrated that the ppGpp sensitivity of rrn P1 promoters depends on the nature and concentration of initiating nucleoside triphosphates (iNTPs). Our results support the notion that the seven rRNA operons are differentially regulated and underline the importance of a concerted activity between ppGpp, DksA and an adequate concentration of the respective iNTP.

Protein aggregation occurs in many age-related neurodegenerative diseases, where it can lead to deposits of naturally occurring proteins in the brain. In case of Creutzfeldt-Jakob disease (CJD), these deposits consist of prion protein (PrP). CJD has three etiologies: spontaneous, genetic, or caused by infection. A polymorphism within the PrP gene is associated with susceptibility of infection. The main event in prion diseases is the conversion of PrP from its naturally occurring isoform to its disease-associated isoform. Here, we present the adaption of a previously reported in vitro conversion system based on hamster recombinant PrP to analyze amyloid fibril formation of human recombinant PrP. We further compare the aggregation characteristics of the human PrP according to the polymorphism variants M129 and V129.