Well, then give more examples of HATs and you can expond on substrate specificity, catalytic mechanism and regulation. Maybe expand into reversing acetylation of internal lysine residues, and how HATs affect oncogenesis.
well being injected into the cytoplasm doesnt mean its going to get translocated into the nucleus to act on the DNA complexes.. but if i suppose there is a nuclear localisation signal, it might then enter the nucleus though. (but i suppose you are not very keen on that ran-gtp mechanism are you?)
so assuming it enters the nucleus, basically you should know that histones are octameric, made up of two h2A, two h2b, two h3, and two h4 histone monomers. and these histones have in them a very high proportion of basic aminoacids, such as lysine, arginine which will be protonated at a physiological pH. DNA has a negatively charged backbone due to the backbone phosphates, and thus histone proteins due to the overall positive charges interact pretty well with DNA, coiling DNA around them.
methylation and acetylation on histone proteins are very commonly seen on lysines, and there are many particular residues that are well researched, i.e. K4, K27 etc. if you are interested you can go search "histone code" and you might find more info. upon acetylation, there is a loss of the positive charge on the lysine side chain, so the histone tails containing lysine will open up, no longer binding to DNA as well, thus allowing then for other genetic activity to go on, i.e. helicase/gyrase binding, further uncoiling etc and recruitment of transcriptional complexes etc.
HOWEVER i have to stress that acetyl transferase activity might not exactly bring about more gene expression. there's this issue on bivalent chromatin, where permissive and non permissive histone modifications are very closely super-imposed on each other. and most of the time the mechanism is not so simple, i.e histone transferrases DONT act on the histones alone. they are actually recruited in as part of a complex, i.e. binding to p300-CREB, binding to p52, binding to NF-kB related proteins etc, and all these have different outcomes.
so how much info do you want for your 10 marks..
and how much $$ do you want to pay me for tuition? :bsmilie: