Introduction to Molecular Cell BiologyTranscription Regulation Dr. Fridoon Jawad Ahmad HEC Foreign Professor King Edward Medical University Visiting Professor LUMS-SSE
Gene Regulation • Some of genes are expressed in all cells all the time. Housekeeping genes are responsible for the routine metabolic functions (e.g. respiration). • Some are expressed as a cell enters a particular pathway of differentiation. • Some are expressed all the time in only those cells that have differentiated in a particular way. • Some are expressed only as conditions around and in the cell change. For example, the arrival of a hormone may turn on/off certain genes in that cell.
Transcription Regulation in E. Coli Inducible & Constitutive Enzymes
Transcription Regulation in E. Coli
Transcription Regulation E. Coli
The Eukaryotic Dilemma For a cell to develop and function properly it must turn on the right genes and right time. Genes are located in the nucleus in a tangled chromatin material wrapped around histones. The structure of chromatin dictates whether a gene can be transcribed not.
DNA Organization Most of DNA is highly ordered and tightly coiled around positively charged histone proteins and is virtually inaccessible to RNA polymerase.
Reorganization In response to specific signal a cell may produce or activate a transcription activator. Transcription activator recognizes and binds a specific sequence of a specific gene and work in conjunction with other proteins that can alter chromatin structure.
Reorganization The alteration may occur by addition of acetyl groups to histones which reduce positive charge. Chromatin remodeling complex can also alter the structure of chromatin to make it accessible to transcription factors that attract RNA Pol.
Reorganization RNA Pol then with help of remodeling complex can move along the gene and make an RNA.
Detailed View Transcribed region has coding information for making proteins and is in copied into RNA. Promoter is upstream of TR and is the core regulatory region where RNA Pol binds. Upstream of promoter are PPE where specific transcription regulatory factors activators or repressors bind here.
Detailed View Activators can recruit the CRC. Many genes also have enhancer (1000 nucleotide away) where specific activators only made by certain cells can bind.
Detailed View Activators recruit TFIID to the promoter. TBP a protein with in TFIID bind TATA sequence (called TATA box) of DNA. Most eukaryote promoters have TATA box, which is located 25bp upstream of start site.
Detailed View TFIID and other factors are required to bind DNA before RNA Pol can recruited. The core transcription complex then initiates transcription.
Transcribing Multiple Genes The simultaneous regulation of widely separated genes is possible through common sequences in their promoters, to which the same regulatory proteins bind.
RNA Processing pre-mRNA (freshly transcribed) is processed to make it functional. 1-Introns are removed during RNA maturation Mature mRNA
The Mechanism Intron-exonbounderies have consensus sequences were snRNPs bind RNA of U1 has complementary bases that bind CS at 5’ exon-intronboundery. RNA of U2 has complementary bases that bind CS near 3’ intron-exonboundery.
RNA Processing 2) The transcribed pre-mRNA is altered by the addition of a G cap (modified GTP) at the 5′ end to protect RNA and facilitate translation. 3) After the last codon a poly A tail (100-300) is added at the 3′ end for export and protection