Protein synthesis and polyamines in thermophiles: Effect of polyamines on nucleic acid maintenance and gene expression

Abstract

Gene expression at both the transcriptional and translational levels is critically dependent upon DNA and RNA structure, particularly in hyperthermophiles, which grow at temperatures above 80 °C. Nucleosome-like structures (histone- bound DNA) from hyperthermophilic Archaea are compacted and stabilized in the presence of multivalent polyamines, suggesting that polyamines play a role in nucleosome maintenance in hyperthermophiles. Multivalent polyamines inhibit the melting of double-stranded DNA and structured RNA. Longer-chain polyamines stabilize double-stranded nucleic acids, whereas branched-chain polyamines stabilize stem-and-loop structures, suggesting that branched-chain polyamines are involved in gene translation. Protein synthesis catalyzed by a cell-free extract of the hyperthermophilic archaeon, Thermococcus kodakarensis, requires the presence of longer- and/or branched-chain polyamines. Translational activity increases in the presence of a variety of linear polyamines and is dependent on chain length. Putrescine and spermidine do not increase translational activity. By contrast, longer polyamines such as homocaldopentamine [3334], caldopentamine [3333], and thermopentamine [3343] increase translational activity. The greatest activity occurs in the presence of N 4 -bis(aminopropyl)spermidine [3(3)(3)4] (abbreviation for the number of methylene CH 2 chain units between NH 2, NH, N, or N +). In vitro experiments using cell extracts from the thermophilic bacterium, Thermus thermophiles, reveal that branched-chain polyamines appear to play a role in peptide bond formation during protein biosynthesis. Thus, it appears that branched-chain polyamines are essential for the proper formation of the 30S initiation complex, which acts as the initial aminoacyl-tRNA in thermophiles.