Termination:

Ultimately, one of three termination codons which is also known as Stop codons becomes positioned in the A site. These are UGA, UAA and UAG. Unlike other codons the prokaryotic cells do not hold aminoacyl-tRNAs complementary to stop codons. Alternatively, one of two release factors RF-1 and RF-2 binds instead. RF-1 recognizes UAG and UAA whereas RF-2 recognizes UGA and UAA.  A third release factor, RF-3, is also needed to assist RF-1/RF-2 interaction with the ribosome.  Therefore RF-1 + RF-3/RF-2 + RF-3 bind depending on the exact termination codon in the A site. RF-1 or RF-2 binds at and near the A site while RF-3 or GTP binds elsewhere on the ribosome. To move the polypeptide to a water molecule alternatively of to aminoacyl-tRNA this release factors cause the peptidyl transferase activity, efficiently cleaving the bond among the polypeptide and tRNA in the P site. To get this, it is very important to realize that the ribosome generally excludes  water from the reaction middle  because  this could otherwise  hydrolyze  the peptidyl-tRNA ester bond and cause premature release of the polypeptide.  The  release  factors  shows  to  work  by  carrying  a water molecule into the peptidyl transferase reaction middle so which the hydrolysis now happen. The free polypeptide now leaves the ribosome followed through the mRNA and free tRNA and the ribosome dissociates into 50S and 30S subunits ready to begin translation again.