 For translation to occur, the ribosome must be recruited to MRNA, yani ke ribosome ko MRNA pe attach hona zeroori hai. Prokreatic MRNAs have a ribosome binding site that recruits the translational machinery. To facilitate binding by a ribosome, many prokreatic ORFs contain a short sequence upstream on the 5 prime side of the MRNA and on the 5 prime side of the start codon and this sequence is called ribosome binding site RBS. This element is also referred to as shin-ol-garno sequence. After the scientists who discovered it by comparing the sequences of multiple MRNAs, the RBS typically located 3 to 9 base pair on the 5 prime side of the start codon is complementary to a sequence located near the 3 prime end of one of the ribosomal RNA components, the 16S ribosomal RNA. So, this RBS sequence is complementary to the 16S ribosomal RNA of the ribosome sequence. As you can see here, this red is the ribosomal binding site because in this MRNA, there are three open reading frames so, there are one, two, three RBSBs so, there are three proteins like this. If you look at this RBS, here the sequence is U-A-A-G-G-A-G-G-U of this RBS sequence and this sequence is the 16S RNA sequence and this sequence is completely complementary to this RBS sequence. So, in this way, this ribosome will be attached here. The RBS base pairs with this RNA thereby aligning the ribosome with the beginning of the ORF. The core of this region of the 16S RNA has the sequence 5 prime this sequence C-C-U-C-C-U-3 prime. Note surprisingly, prokaryotic RBS are most often a subset of the sequence A-G-G-A-G-G. The extent of complementarity and the spacing between the RBS and the start codon has a strong influence on how actively a particular ORF is translated. So, this RBS has a complementarity with the 16S RNA and its distance from the start codon as it is before the start codon and how much distance it has. These two points complementarity and distance are very important for efficient translation. High complementarity and proper spacing for active translation whereas limited complementarity and poor spacing generally sport lower levels of translation. Some prokaryotic ORFs lack a strong RBS but are nonetheless actively translated. These ORFs are not the first ORF in an mRNA but instead are located just after another ORF in a polycystronic message. And these are the cases which in one mRNA one ORF is finished and the next ORF is the same. So, the first ORF is finished and since the next ORF has started, the ribosome attached will remain the same and after translating one protein the next ORF or the next protein will start reading. So, in this case, there is no need for RBS. In these cases, the start codon of the downstream ORF often overlaps the 3 prime end of the upstream ORF 5 prime end 2nd ORF 3 prime end with this way overlaps. Thus, the ribosome that has just completed translating the upstream ORF is positioned to begin translating from the start codon of the downstream ORF. This phenomena of linked translation between overlapping ORFs is known as translational coupling. So, in this situation translation of the downstream ORF requires translation of the upstream ORF. So, if upstream ORF is translated, then downstream ORF is translated. Otherwise, this cannot be translated. Indeed, with two translationally coupled genes a mutation that leads to a premature stop codon in the upstream ORF also prevents translation of the downstream ORF. So, in this case translation is coupled and after one ORF the second ORF begins. But in the first ORF i.e. the first upstream ORF if there is a mutation and from this mutation the stop codon is introduced in this ORF. So, this means that the translation of the stop and the next ORF cannot be read.