Ara operon

Mcrobial genetics

1. ara operon presentation Dr. P. Suganya Assistant Professor Department of Biotechnology Sri Kaliswari college (autonomous), sivakasi

2. operon FRANCIS JACOB And JACQUES MONAD 1961 Explained that gene regulation is by operon model 2

3. The Operon Consist of regulatory gene structural gene operator and promoter site This 3 basic DNA components 3

4. 3 BASIC DNA COMPONENTS Structural genes – The genes that ara co-regulated by the operon Operator –A segment of DNA to which a repressor binds Promoter – A Nucleotide sequence that enables a gene to be transcribed 4

5. Ara Operon The L-arabinose operon , also called ara operon ,is a gene sequence encoding enzymes needed for tha catabolism of arabinose to xylulose 5- phosphate ,an intermediate of the pentose phosphate pathway. It has both positive and negative regulation . T he genes araBAD and araC,are transcribed in opposite directions 5

6. Structure of ara operon 6

7. arabinose as a corbon source by converting it into Xylulose-5- phosphate an intermediate in the pentose phosphate pathway. The ara operon codes for 3 enzymes .that are required to catalyze the metabolism of arabinose encoded by 3 genes araB,araA , ara D.It is called ara BAD 7 Structural genes

8. Control or regulatory genes The three structural genes in an operon is regulated by the ara C gene product . The ara C gene is present near by operator gene and transcribed from its own promoter which is nearby ara O1 . The ara c is transcribed in opposite derection to ara BAD gene the ara c produces repressor molecules . Ara operon consists of two regulatory operator site , ara O1 and ara O2 . 8

9. Mechanism of regulation of ara-operon The regulatory protein ara c ,encoded by ara c gene mediates both possitive and negative control. Binding of a singnal molecule to the ara c protein alters the conformational change from the repressor form to an activator form. The ara c repressor protein regulates its own synthesis ,by binding at ara O1.the ara c represses its own transcription . 9

10. Negative regulation Arabinose livels ara low and glucose levels are high,ara c protein binds to the both ara I and ara O2 and these sites together to form a DNA loop of about 210 base paris . The arabinose operon is switched off. These events block the access of RNA polymerase to the PBAD promoter( which is a very weak promoter) 10

11. Negative regulation structure 11

12. Positive regulation The arabinose concentration is high or when glucose concentration is very low ara c protein binds to the arabinose ,changing its conformation leading to the binding of ara c reprossor protein to the ara O1 and ara I The DNA loop is opened and the transcription of structural genes ara BAD mRNA synthesis enzymes to metabolise arabinose The arabionse operon is switched on 12

13. Structure of positive regulation 13

14. Thank you