Thermococcus, Methanococcus and Methano-bacterium exemplify
(1) bacteria whose DNA is relaxed or positively supercoiled but which have a cytoskeleton as well as mitochondria
(2) bacteria that contain a cytoskeleton and ribosomes
(3) archaebacteria that contains protein homologous to eukaryotic core histones
(4) archaebacteria that lack any histones resembling those found in eukaryotes but whose DNA is negatively supercoiled
(4) Thermococcus, Methanococcus and Methanobacterium exemplify archaebacteria that lack any histones resembling those found in eukaryotes but whose DNA is negatively supercoiled. Archaebacteria do not have a nucleus, the genetic material floats freely in the cytoplasm. They consist of ribosomal RNA. DNA contains a single, circular molecule, which is compact and tightly wound. No protein is associated with DNA. The archaebacterial cell may contain plasmids, which are small, circular pieces DNA and have a highly negatively supercoiled DNA.
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