Chemical and functional aspects of posttranslational modification of proteins.

This paper reviews the chemical and functional aspects of the posttranslational modifications of proteins, which are achieved by the addition of various groups to the side chain of the amino acid residue backbone of proteins. It describes the main prosthetic groups and the interaction of these groups and the apoenzyme in the process of catalysis, using pyridoxal catalysis as an example. Much attention is paid to the role of posttranslational modification of proteins in the regulation of biochemical processes in live organisms, and especially to the role of protein kinases and their respective phosphotases. Methylation and acetylation reactions and their role in the "histone code", which regulates genome expression on the transcription level, are also reviewed. This paper also describes the modification of proteins by large hydrophobic residues and their role in the function of membrane-associated proteins. Much attention is paid to the glycosylation of proteins, which leads to the formation of glycoproteins. We also describe the main non-enzymatic protein modifications such as glycation, homocysteination, and desamida-tion of amide residues in dibasic acids.

Photoanalogues of the initiation substrates of the RNA polymerase II, 5-azido-2-nitrobenzoyl derivatives of the ATP gamma-amidophosphate: the possible photoinduced degradation of the functional group to an N-arylhydroxylamine.

Photoanlogues of the initiation substrates of the RNA polymerase II, N3ArNH(CH2)(n)NHpppA where N3Ar is 5-azido-2-nitrobenzoyl group (n = 2 or 4) were synthesized, allowing the preparation of photoreactive oligonucleotides in situ by RNA polymerase II for application as photolabels. Photolysis of p-nitro-substituted aromatic azide in aqueous medium was investigated. Using the azoxy-coupling reaction it was possible to determine whether a nitrene or p-nitrophenyl hydroxylamine azoxy compound is the trappable intermediate that is generated at ambient temperature in aqueous solution.

Affinity labeling of RNA-polymerase II in the transcriptionally active complex by a phosphorylating analog of the initiation substrate.

Affinity modification of RNA-polymerase II by a phosphorylating analog of the initiation substrate carrying a zwitterionic 5;-terminal phosphate group with a 4-N,N-dimethylaminopyridine residue (DMAP-pA) was studied during specific transcription initiation controlled by the late adenoviral promotor. Super-selective affinity labeling and standard conditions of affinity modification resulted in labeling a polypeptide with molecular weight corresponding to that of the third subunit of the enzyme, RPB3 (45 kD). The initiation substrate (ATP) protects RNA-polymerase II from modification. The third subunit may be involved in the formation of the substrate-binding site of the enzyme.