Ribosomal and DNA binding proteins of the thermoacidophilic archaebacterium Sulfolobus acidocaldarius

Abstract

Ribosomal and DNA binding proteins have been extracted from the thermoacidophilic archaebacterium Sulfolobus acidocaldarius grown at 75–80°C and pH 4.8-4.5. In order to obtain large amounts of material for structural studies we have optimized the fermentation conditions. Using a feed-batch regime it was possible to obtain a yield of 5–8 g/liter of actively growing bacteria in 2–3 days. The ribosomal proteins were characterized by two-dimensional gel electrophoresis, and the effect of different preparative procedures for the isolation of ribosomes on the two-dimensional gel pattern of the ribosomal proteins was assessed. A set of small, basic and abundant DNA binding proteins was purified under conditions which protect their native structure. In contrast to most eubacteria, where only a single, small and basic protein (DNA binding protein II or HU) is present, S. acidocaldarius has several proteins with three different molecular mass values, namely 7 kDa, 8 kDa and 10 kDa. Within each of these three size classes at least two proteins are found which differ in charge. The DNA binding character of these proteins was verified using several binding assays. The affinity for double-stranded DNA increases with increasing molecular mass vlaues. The Stokes radii determined by analytical gel filtration indicate that the 7 and 8 kDa proteins occur as monomers and the 10 kDa proteins possibly as dimers.