Using a quantitative biochemical approach, I will test the possibility that nucleosome retention at CpG islands is an indirect consequence of high intrinsic affinities of protamines
for GC-poor DNA.
The replacement of histones with protamines is a crucial step in spermatogenesis.
Human protamines and the developing spermatid: their structure, function, expression and relationship with ma le iniertility.
In particular, it was not clear how a molecular transition from a lysine-rich protein precursor (H1 histone) to the arginine-rich protamines might have taken place.
On the basis of these early studies, Bloch proposed an initial classification of SNBPs that distinguished five major groups: (1) The Salmo type consisting of relatively small arginine-rich "monoprotamines" found in fish such as salmon; (2) the mouse/grasshopper type consisting of cysteine-containing arginine-rich "stable protamines"; (3) the Mytilus type, with proteins intermediate between those of protamines and histones with respect to composition of arginine and lysine; (4) the Rana type in which mature sperm retains somatic-like chromosomal proteins; and (5) the crab type in which the DNA in the mature sperm apparently lacks any chromosomal proteins and as a result the nucleus appears large and swollen.
In a second study, Mohamed Hammadeh from the University of the Saarland in Germany, and colleagues, examined the concentrations of two proteins called protamines
P1 and P2, which are crucial to the formation of chromosomes during cell division.
A second study in Germany looked at the levels of two protamines
- P1 and P2 - in the sperm of smokers and non-smokers.
In the second study, researchers looked at specific proteins called protamines
in the sperm of men who smoked and compared them with the protamines
These proteins are then replaced by more basic proteins named protamine (P1, P2), which are responsible for the final condensation and stabilization of sperm DNA (34) Sperm DNA interacts with protamines so that it converts the coiling of sperm DNA into toroidal subunits so called as "Doughnut loops" (35).
The histones should be replaced by protamines during sperm DNA packaging for more chromatin condensation (39).
The formation of mature spermatozoa involves a series of mitosis, meiosis, changes in cytoplasmic structure, topological rearrangements, alteration in transcription, replacement of histones with transition proteins and the final addition of protamines
leading to highly condensed insoluble and stable chromatin.
Our initial experiments revealed that histones and protamines
generate a significant interaction with the IRMA for CRH and ACTH.