The document summarizes regulation of gene expression in prokaryotes and eukaryotes. In prokaryotes, genes are organized into operons containing a promoter, operator, and multiple coding sequences. The lac operon in E.coli contains genes regulated by the repressor protein LacI and induced by lactose. In eukaryotes, gene expression is regulated at multiple levels including transcription, RNA processing, transport, translation and degradation. Mechanisms include histone modification, DNA methylation, hormone signaling, polyadenylation, splicing, transport and protein degradation.

1. REGULATION OF GENE EXPRESSION IN PROKARYOTES & EUKARYOTES Lecture By RAVI DHANDE Lecturer, Department of Botany Shri Shivaji College, Akot [email_address]

3. Central theme of protein synthesis

4. Operon - what is it? Cluster of genes in which expression is regulated by operator-repressor protein interactions, operator region, and the promoter. Contents of an operon: Promoter Regulator Operator (controlling site) Coding sequences (Adjacent polycystronic coding sequences/ polygenic mRNA ) Terminator Inducer , Induction? Inducible gene? Repressor, Repression? Repressible gene?

5. Organization of an inducible gene containing an operon

7. General organization of the lac operon of wild-type E. coli . Order of controlling elements and genes: lacI : promoter- lacI -terminator operon: promoter-operator- lacZ - lacY - lacA- terminator

8. Organization of lac operon size mRNA Lac i Lac Z Lac Y Lac A Polypeptide 38 kd 116 kd 30 kd 30 kd Active protein Tetramer 152 kd Tetramer 500 kd Monomer 30 kd Dimer 60 kd Function Repressor B- galactosidase Permease Transacetylase

9. Functional state of the E. coli lac operon in the absence of lactose

10. Functional state of the E. coli lac operon growing on lactose

12. Translation of lac operon in wild type and mutant E. coli

15. Base pair sequence of controlling sites, promoter, and operator for lac operon of E. coli .

16. Positive control of the lac operon glucose glucose cAMP cAMP - CAP cAMP –CAP-RNA POL COMPEX Gene turn on cAMP NO cAMP –CAP NO cAMP –CAP-RNA POL COMPEX Gene turn off

17. REGULATION OF GENE EXPRESSION IN EUKARYOTES Central theme of protein synthesis

18. Levels of Eukaryotic Gene Regulation Transcription RNA processing mRNA transport mRNA translation mRNA degradation Protein degradation

21. DNA methylation and transcription control Methylation occurs most often in symmetrical CG sequences. Transcriptionally active genes possess significantly lower levels of methylated DNA than inactive genes. Methylation leads to suppression of genes. Demethylation leads to expression of genes.

22. Hormone for regulation of transcription Cells of higher eukaryotes are specialized and generally shielded from rapid changes in the external environment. Hormone signals are one mechanism for regulating transcription in response to demands of the environment. Hormones deliver signals in two different ways: Steroid hormones pass through the cell membrane and bind cytoplasmic receptors, which together bind directly to DNA and regulate gene expression. Polypeptide hormones bind at the cell surface and activate transmembrane enzymes to produce second messengers (such as cAMP) that activate gene transcription .

27. Post-translational control - protein degradation Proteins can be short-lived or long-lived Protein degradation in eukaryotes requires a protein co-factor that binds to proteins and identifies them for degradation by proteolytic enzymes. Amino acid at the N-terminus is correlated with protein stability and determines rate of co-factor binding. Arg, Lys, Phe, Leu, Trp 1/2 life ≤3 minutes Cys, Ala, Ser, Thr, Gly, Val, Pro, Met 1/2 life ≥ 20 hours