There are many toxic compounds present in the environment which harm the genes of the plants are called genotoxic compounds. the presence of these compounds is indicated by certain signals.
2. Bioindicators
๏ถBioindicators are defined as organisms used to
monitors the health of, or changes in, their
surroundings or ecosystem.
๏ถThis can be plants, animals or bacteria that
regularly produce certain molecular signals in
response to changes in their environmental
conditions.
๏ถBioindicators are also known as biomarkers.
3. Genotoxic Compounds
๏ถToxic to life
๏ถDNA damaging compounds
๏ถDifficult to metabolize as they contain
molecular arrangement that are not normally
encountered in nature.
๏ถe.g., Ethyl methane sulphate (EMS), methyl
methane sulphate (MMS), mitomycin C (MMC),
hydrogen peroxide, formaldehyde, N-methyl-N-
nitro-N-nitrosoguanidine.
4. Single stranded and double stranded DNA damage
potentially caused by genotoxic compounds.
6. How genotoxic compounds affect DNA?
Replication
Genotoxic compounds
Activation of SOS Response Gene
Rec A
Rec A โSS DNA
7. SOS Response
Rec A autocatalytic activity
Cleavage of Lex A repressor at Ala-Gly peptide bond
SOS response gene express
๏ฑSOS induces damage inducible (din) gene or sos
gene has 20 nucleotide long โSOS-boxโ near its
promoter/operator site, to which Lex A repressor
protein bound, preventing RNA polymerase binding
and gene expresson.
8. SOS response can be used as
Bioindicator
Construct a plasmid vector in which din gene
promoter fused with lac Z gene .
โข In normal condition lacZ gene not express due to
genotoxic compound.
โข But din gene express in the presence of toxic
compound
โข When lacZ gene construct with din promotor it
express in this condition.
9. Detection of SOS-Induced Genes
din gene Lac Z gene
P
P
Din gene
lac Z gene
Vector
Transfer into E. coli
10. Detection of SOS-Induced Genes
DNA damage No expression of ฮฒ-galactosidase
๏งIf Lac Z gene expressed with din promoter then formation
of ฮฒ-galactosidase start in response to DNA damage.
๏งIf Lac Z gene replaced by GFP gene then it produces GFP.
๏งWith the help of fluorescent GFP present can be detected.