Molecular Biology of the Archaea
Chromosomes and DNA Replication
DNA negative supercoil: DNA gyrase in bacteria, Histone proteins in eukaryotes.
Eukaryotic histones consist of eight proteins, Archae 4 proteins (tetrasomes) and are shorter. Other features are similar to
eukaryotes.
In some hyperthermophal archaea, positive super helixes are formed by reverse gyrase enzyme. Denaturation of DNA at high temperature is thus prevented.
Molecular Biology of the Archaea
genome replication in bacteria, there is only one origin region, and two Sulfolobus and three origin regions from Halobacterium. There are many replication origins in the eukaryotic chromosome.
Archaea enzymes involved in replication are similar to eukaryotes.
In all organisms, DNA polymerase is structurally divided into three groups: A, B and C. Bacteria are C (Pol III) for replication, A and B for repair; Archaea and Eukaryotes use others to replicate B in replication.
Molecular Biology of the Archaea
Transcription
In eukaryotes, rRNA RNA polymerase I, mRNA RNA polymerase II,
tRNA and small rRNA RNA polymerase III
Each of these three RNA polymerases recognizes the promoter region of a particular group of genes. Most of the genes in
eukaryotes are transcribed by RNA polymerase II.
RNA polymerases in eukaryotes are more complex than bacteria.
Molecular Biology of the Archaea
As in Bacteria, Archaea has a single RNA polymerase.
This enzyme resembles the RNA polymerase II enzyme in eukaryotes rather than bacteria.
This enzyme contains a 6-8-base AT rich TATA box (TATA box) in the promoter region before the initiation of transcription.
This region is similar to the Pribnow box in bacteria.
The rifamycin antibiotic binds to the β subunit of RNA polymerase in bacteria, preventing transcription and is ineffective to archaea and eukaryotes.
Amanitin chemical affects the enzyme RNA
polymerase II and stops transcription in eukaryotes.
The rho proteins that lead to termination of transcription in bacteria were not found in the background.
Inverse repetitions, like bacteria, terminate in some Archaea.
RNA Processing
In eukaryotes, the first synthesized RNA is processed to form mature mRNA.
In this process, the introns in the RNA are cut and the exons combined. In this process called splicing, a
complex consisting of RNA and protein called spliceosome works.
Although both prokaryotic and eukaryotic genes have intron regions, RNA is processed only in eukaryotes. The nucleus is then attached to the 5 cap end of this mature mRNA and the poly A tail to the 3 ’end.
RNA molecules showing enzymatic activity.
It was first found in their study with Sidney Altman and Thomas Cech (Tetrahymena thermophila).
They won the Nobel Prize (chemistry) in 1989.
Ribozyme (ribonucleic acid enzyme)
Archaea introns
Archaea tRNA and rRNA encoding genes have introns processed in this way.
A specific endoribonuclease recognizes
exon-intron junctions and removes introns two stages. In the first stage endonuclease is cut, in the second stage ligases are
ligated.
The introns in the folded tRNA are cut at the points indicated by the arrow in figure b, forming the annular intron and the tRNA.
Protein Sythesis
There are 78 proteins in eukaryotic ribosomal RNA.
Of these, 34 are found in bacteria and Archaea
sites, 33 in Archaea sites, and the remaining 11 are found only in eukaryotes.
Archaea translation factors are not as complex as in eukaryotes, but more similar to eukaryotes than
bacteria.
Shine dalgarno sequence is present in bacteria and archaea, not in eukaryotes.
The first synthesized amino acid is methionine in archaea and eukaryotes.
