They proposed the ribosome filter hypothesis to explain the regulatory functions of ribosomes. Ribosomes and ribosomal subunits are found in these bodies. Modifications to core ribosomal proteins may give rise to the formation of heterogeneous ribosomes. The ribosomes in chloroplasts are similar to bacterial ribosomes. It is structurally and functionally related to the 30S subunit of 70S prokaryotic ribosomes. I site in eukaryotic or archaeal ribosomes has not yet been confirmed. Tetracycline binds to the 30S and 50S subunit of microbial ribosomes. Protein biosynthesis is most commonly performed by ribosomes in cells. Ribosome biogenesis is the process of making ribosomes. Messenger RNA acts to carry genetic sequence information between DNA and ribosomes, directing protein synthesis. The nucleolus, which makes ribosomes in the cell, also disappears. Many types of cells export proteins produced by ribosomes attached to the rough ER. Examples are tRNA, ribosomes, ribozymes, and riboswitches. The ssRNA is then mass translated by host ribosomes, producing necessary viral proteins. Protein synthesis occurs during the process of translation on ribosomes.