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= Genome =

Nowadays, Sulfolobus solfataricus is the most studied microrganism from a molecular, genetic and biochemical point of view for its ability to thrive in extreme environments; it is easily cultivable in laboratory; moreover, it can exchange genetic material through processes of transformation, transduction and conjugation.

The major research on these microorganisms concerns the thermostability of proteins that normally denature at high temperature.Scientists from the European Union and Canada managed to completely sequence the genome of S. solfataricus in 2001. One-third of S. solfataricus encoded proteins have no homologs in other genomes.On a single chromosome there are 2,992,245 base pairs which encode for 2,977 proteins and copious RNAs. Regarding the remaining encoded proteins, 40% are specific to Archaea, 12% are shared with Bacteria and 2.3% are shared with Eukarya ;33% of these proteins is encoded exclusively in Sulfolobus. A high number of ORFs (open reading frame) are highly similar in Thermoplasma.

Small nucleolar RNAs (snoRNAs) ,already present in eukaryotes, have also been identified in S.Solfataricus and S.acidolcaldarius. They are already known for the role they play in posttranscriptional modifications and removal of introns from ribosomal RNA in Eucarya.

The genome of Sulfolobus is characterised by the presence of short tandem repeats,insertion and repetitive elements, it has a wide range of diversity as it has 200 different ISs insertion sequence elements.

Reverse Gyrase : thermophilic enzyme
The stabilisation of the double helix against denaturation, in the Archaea, is due to the presence of a particular specific thermophilic enzyme,reverse gyrase It was discovered in hyperthermophilic and thermophilic Archaea and Bacteria .There are two genes in Sulfolobus that each encode a reverse gyrase. It is defined atypical Dna topoisomerases and the basic activity consists in the production of positive supercoils in a closed circular Dna.Positive supercoiling is important to prevent the formation of open complexes. Reverse gyrases are composed of two domains : the first one is the helicase like and second one is the topoisomerase I. A possible role of reverse gyrase could be the use of positive supercoiling to assemble chromatin-like structures. In 1997 scientists discovered another important feature of Sulfolobus : this microrganism contains a type-II topoisomerase, called TopoVI, whose A subunit is homologous to the meiotic recombination factor, Spo11 which plays a predominant role initiation of meiotic recombination in all Eucarya  S. solfataricus is composed of three topoisomerases of type I, TopA and two reverse gyrases, TopR1 and TopR2, and one topoisomerase of type II, TopoVI.

Dna binding protein : Alba ,Cren7,Sso7d
In the Phylum Crenarchaeota there are three proteins that bind the minor groove of Dna like histones:Alba, Cren7, and Sso7d, that are modified after the translation process .These are small and have been found in several strains of Sulfolobus but not in other genome.Chromatin protein in Sulfolobus represent 1-5% of the total. They can have both structural and regulatory functions. These look like human HMG-box proteins, because of their influence on genomes, for the expression and the stability, and on epigenetic processes. In species lacking histones they can be acetylated and methylated like eukaryotic histones. Sulfolobus strains present different peculiar DNA binding proteins, such as the Sso7d protein family. They stabilize the double helix, preventing denaturation at high temperature thus promoting annealing above the melting point.

The major component of archael chromatin is represented by Sac10b family protein known as Alba (Acetylation lowers binding affinity ). These proteins are small, basic and dimeric nucleic acid-binding proteins.Furthermore, it is conserved in most sequenced archeal genomes. The acetylation state of Alba, as an example, affects promoter access and transcription in vitro, whereas the methylation state of another Sulfolobus chromatin protein, Sso7D, is altered by culture temperature.

The work of Wolfram Zillig’s group, representing early evidence of the eukaryotic characteristics of the transcription in Archea, has since made Sulfolobus an ideal model system for transcription studies .Recent studies in Sulfolobus, in addition to other archaeal species mainly focus on the composition, function and regulation of the transcription machinery in these organisms and on fundamental conserved aspects of this process in both Eucarya and Archaea