MOLECULES AT THE EXTERNAL NUCLEAR SURFACE Sialic Acid of Nuclear Membranes and Electrophoretic Mobility of Isolated Nuclei and Nucleoli

The molecules occurring as terminal residues on the external surfaces of nuclei prepared from rat liver by either sucrose-CaC12 or citric acid methods and nucleoli derived from the sucrose-CaC1 2 nuclei were studied chemically and electrokinetically . In 0.0145 M NaCl, 4.50/,) sorbitol, and 0 .6 mM NaHCO3 with pH 7 .2 t 0.1 at 25°C, the sucrose-CaC12 nuclei had an electrophoretic mobility of -1 .92 ,um/s/V/cm, the citric acid nuclei, -1 .63 μm/s/V/cm, and the nucleoli, -2 .53 μm/s/V/cm . The citric acid nuclei and the nucleoli contained no measurable sialic acid . The sucrose-CaC12 nuclei contained 0.7 pmol of sialic acid/mg nuclear protein ; this was essentially located in the nuclear envelope . Treatment of these nuclei with 50 μg neuraminidase/mg protein resulted in release of 0.63 pmol of sialic acid/mg nuclear protein ; treatment with 1 % trypsin caused release of 0 .39 nmol of the sialic acid/mg nuclear protein . The pH-mobility curves for the particles indicated the sucrose-CaC12 nuclei surface had an acid-dissociable group of pK 2.7 while the pK for the nucleoli was considerably lower . Nucleoli treated with 50 μg neuraminidase/mg particle protein had a mobility of -2 .53 Am/s/V/cm while sucrose-CaC12 nuclei similarly treated had a mobility of -1 .41 μm/s/V/cm. Hyaluronidase at 50 μg/mg protein had no effect on nucleoli mobility but decreased the sucrose-CaC12 nuclei mobility to -1 .79 M.m/s/V/cm . Trypsin at 1 % elevated the electrophoretic mobility of the sucrose-CaC12 nuclei slightly but decreased the mobility of the nucleoli to -2 .09 μm/s/V/cm. DNase at 50 Ag/mg protein had no effect on the mobility of the isolated sucrose-CaC12 nuclei but decreased the electrophoretic mobility of the nucleoli to -1 .21 μm/s/V/cm. RNase at 50 μg/mg protein also had no effect on the electrophoretic mobility of the sucrose-CaC12 nuclei but decreased the nucleoli mobility to -2 .10 μm/s/V/cm . Concanavalin A at 50 Ag/mg protein did not alter the nucleoli electrophoretic mobility but decreased the sucrose-CaC1 2 nuclei electrophoretic mobility to -1 .64 μm/s/V/cm . The results are interpreted to mean that the sucrose-CaC1 2 nuclear external surface contains terminal sialic acid residues in trypsin-sensitive glycoproteins, contains small amounts of hyaluronic acid, is completely devoid of nucleic acids, and binds concanavalin A . The nucleolus surface is interpreted to contain a complex made up of protein, RNA, and primarily DNA, to be devoid of sialic acid and hyaluronic acid, and not to bind concanavalin A. THE JOURNAL OF CELL BIOLOGY • VOLUME 59, 1978 . pages 6 0 1 -614 601 on Jauary 1, 2018 jcb.rress.org D ow nladed fom