I. Vibrio symbionts are selectively “winnowed from external milieu
a. Symbiont monoculture becomes established in light organ
b. Es114 strain is the strain that can colonize light organs
c. Rscs sits in membrane where it detects specific signal (change in the
environment) and auto phosphorates on interior side of protein that initiates
cascade where phosphate transfers phosphate to SypG
i. SypG is activator gene: Activates gene transcription in positive way
1. Activates sypa-R lotus
ii. SypA-R encodes genes for exopolysaccharides production (sugar
produced and used outside cell)
1. Syp exopolysaccharides are sticky and enable vibrio to create
biofilms
iii. Loss of rscS prevents vibrio from colonizing its host
1. One single gene determines host suitability
d. Major modes of regulation
i. Gene Expression: Transcription of gene into mRNA followed by
translation of mRNA into protein
1. Regulate at different points in process
2. Some proteins are constitutive, being needed at the same level at
the same time
a. If environment doesn’t change much
b. Very rare
3. Microbial genomes encode many proteins that aren’t needed all
the time
ii. Two major levels of regulation in cell
1. One controls ACTIITY of preexisting enzymes
a. Very rapid process
b. Posttranslational regulation
2. One regulates the AMOUNT of an enzyme
a. Regulation translation and transcription
b. Slower process
c. Major mode in prokaryotes
d. Turning off before it can even exist
3. Transcriptional regulation involves DNA-binding proteins
a. Histone, DNA polymerase 1,2,3, Response regulators
b. Interact in some sequence specific manner
i. Recognize specific sequence in DNA
ii. Interactions between amino acid side chains and
chemical groups on bases and sugar
c. Major groove of DNA is main site of protein binding
d. Proteins usually homomeric: Composed of two identical
polypeptides
i. Interact with inverted repeats
