Question

Are histones present in prokaryotes?

Answer 1

Prokaryotic cells are represented by bacteria, cyanobacteria or Blue Green Algae, mycoplasma or PPLOs, Spirochaete and Rickettsiae. The prokaryotic cells are generally far smaller than eukaryotic cells. However, they multiply more rapidly than most of the eukaryotic cells. Prokaryotic cells have much variation in size and shape.

Complete answer:
The proteins promoting the DNA packaging into chromatin fibres are called histones. They are positively charged and possess several arginine and lysine amino acids binding to the DNA having negatively charged.

In prokaryotes a membrane bound well defined nucleus is absent. Their genetic material is naked (i.e. not complexed with protein molecules). It is also not packed in the chromosomes. The genetic material of prokaryotes consists of a long double stranded DNA molecule and is called nucleoid, nuclear body or genophore. In some cases RNA and small amounts of protein are also present. The length of a DNA strand may be 250-700 times the length of the cell. The DNA is repeatedly folded to effectively fit within the nuclear region.

It is highly looped and coiled with the help of nucleoid proteins. Nucleoid proteins are different from histone proteins that are present in eukaryotes. Through the mesosome the nucleoid is connected to the plasma membrane. It is therefore believed that the membrane may be involved in the separation of duplicated DNA into daughter cells during division.
By the above discussion it is cleared that the histones are present in eukaryotes not in prokaryotes.

Note: The prokaryotic cells may possess additional rings of DNA called plasmids. The plasmids can replicate independently. Some of them carry important genes like NIF gene, fertility factor and drug resistance factor. At times, plasmid may get temporarily associated with the nuclear body and is called episome.