Summary

1. MG045 and UU110 are the hypothetical proteins which might play a role as the binding protein in Spermidine / Putrescine ABC transporters system.

2. Inhibition of spermidine uptake in Escherichia coli, which occurs in the presence of accumulated polyamines, has been studied using the spermidine uptake operon consisting of the potA, -B, -C, and -D genes. Transcription of the potABCD operon was inhibited by PotD, a spermidine-binding protein usually found in the periplasm, and the inhibitory effect of PotD was increased by spermidine. Transcription was not affected by bovine serum albumin, PotA, or PotF, suggesting that the effects of PotD are specific to the PotD protein. Experimental results indicate that PotD precursor can also inhibit spermidine transport. The amino acid residues in PotD that are involved in its interaction with the potABCD operon were determined using mutated PotD proteins. Thr-35 and Ser-85 of PotD were found to be important for this interaction. These results suggest that transcription of the spermidine transport (potABCD) operon is inhibited in vivo by PotD precursor rather than PotD through its binding to two regions close to the transcriptional initiation site of the operon. (J Biol Chem 1999 Jan 22;274(4):1942-8 Transcriptional inhibition of the operon for the spermidine uptake system by the substrate-binding protein PotD. Antognoni F, Del Duca S, Kuraishi A, Kawabe E, Fukuchi-Shimogori T, Kashiwagi K, Igarashi K PMID: 9890949, UI: 99107839).