The polyadenylation reaction passes through two stages. 

First, a rather short oligo(A) sequence (10 residues) is added to the 3’ end. This reaction is absolutely dependent on the AAUAAA sequence and poly(A) polymerase performs it under the direction of the specificity factor. 

In the second phase, the nuclear poly(A) binding protein (PABP II) binds the oligo(A) tail to allow extension of the poly(A) tail to the full 200 residue length.

TLS Online TPP Program

#Id: 3856

#Unit 5. Developmental Biology

Dictyostelium can utilize one of three survival strategies when food starvation-

(1) Microcyst formation, favoured in dark & wet conditions, or ammonia levels are high.
(2) Zygote formation, favoured in dark & wet conditions, & triggered by ethylene produced by the cells.
(3) Cell aggregation & differentiation

TLS Online TPP Program

#Id: 3857

#Unit 5. Developmental Biology

Phosphorylation of RegA is mediated by sensor histidine kinases/phosphatases which either phosphorylate or dephosphorylate themselves on a histidine residue when a signal molecule binds to their sensor domain.

TLS Online TPP Program

#Id: 3858

#Unit 5. Developmental Biology

Cell Aggregation & Differentiation is common to all Dictyostelids.
It consists of an interconnected programme of cell movement and cell differentiation.

TLS Online TPP Program

#Id: 3859

#Unit 5. Developmental Biology

The binding of ammonia to the sensor domain of DhkC leads to the activation of its histidine kinase activity and to the autophosphorylation of a DhkC histidine residue.

TLS Online TPP Program

#Id: 3860

#Unit 5. Developmental Biology

The phosphoryl group is transferred,

From histidine residue of DhkC  aspartate of DhkC histidine in phospho-transfer intermediate RdeA aspartate of RR of RegA

TLS Online TPP Program

#Id: 3861

#Unit 5. Developmental Biology

When the ratio of PSF relative to that of bacteria exceeds a certain threshold, cells stop proliferating and initiate the expression of genes that are required for their aggregation.