Properties of Membrane-bound Ribosomes in Reticulocytes

Nature and origins of chromatin-associated ribonucleic acid of avian reticulocytes

“…When purified chromatin and the membrane fraction are subjected to hot phenol extraction, both yield high molecular weight RNA containing 18S and 28S material (Figure 4D,E), indicating that ribosomes associated with membrane are the major source of chromatin associated RNA in avain reticulocytes. A specific class of membrane associated RNA, termed "membron" RNA, has also been reported (Shapot and Davidova, 1971), but it is difficult to eliminate the possibility that this RNA arises from degradation of rRNA. It is worth noting that cRNA isolated from rat ascites cells by Bonner (1968,1971) was obtained from the membranous material separated from chromatin by centrifugation through 1.7 m sucrose.…”

“…It is therefore likely that rRNA present in chromatin preparations comes from ribosomes bound to membranes. Ribosome attachment to membranes in vitro and in vivo is well documented (Schreml and Burka, 1968;Burka and Schickling, 1970;Attardi et al, 1969;Rosbash and Penman, 1971a,b). It is shown here (Figure 4D,E) that high molecular weight RNA exists in membrane derived from avian erythroid chromatin and other data suggest that sufficient membrane is also present in purified chromatin to account for levels of RNA found in preparations pelleted through 1.7 m sucrose (Harlow et al, 1972).…”

Attachment of reticulocyte ribosomes to erythroid cell membranes in vitro

“…The analytical and preparative methods used have been described in detail in previous communications (Schreml and Burka, 1968; Burka, ,1969.…”

“…The number of these sites, which are not destroyed by exposure to trypsin, declines with increasing cell maturity. Free ribosomes L Approximately 18% of ribosomes in reticulocytes of all degrees of maturity is closely bound to the cell membrane (Schreml and Burka, 1968; . The significance of the binding, as well as the exact means of attachment, remains unknown (Schreml and Burka, 1968;Hendler, 1965).…”

“…Free ribosomes L Approximately 18% of ribosomes in reticulocytes of all degrees of maturity is closely bound to the cell membrane (Schreml and Burka, 1968; . The significance of the binding, as well as the exact means of attachment, remains unknown (Schreml and Burka, 1968;Hendler, 1965). Both pulse-labeling experiments and exchange studies in an in vitro system (Burka, 1969) indicate that these membrane-bound erythroid cell ribosomes freely exchange with the pool of free ribosomes.…”