Nuclear pore flow rate of ribosomal RNA and chain growth rate of its precursor during oogenesis of Xenopus laevis

Abstract

The numb er of ribosomal RNA mol ecules which are transferred through an average nuclear pore complex per minute into the cytoplasm (nuclear pore flow rate, NPFR) during oocyte growth of Xenopus laevis is estimated. The NPFR calculations are based on determinations of the increase of cytoplasm ic rRNA conten t during defined time intervals and of the total number of pore complexes in the respective oogenesis stages. In the mid-la mpbrush stage (500:"700 I'm oocyte diameter) the NPFR is maximal with 2.62 rRNA molecules/ pore/ minute. Then it decreases to zero at the end of oogenesis. The nucleocytoplasmic RNA f10w rates determined are compared with corresponding va lues of other cell types. The molecular weight of the rRNA precursor transcribed in t he extrachromosomal nucleoli of Xenopus la mpbrush stage oocytes is determined by acrylamide ge l electrophoresis to be 2.5 x 10· daltons. From the temporal increase of cytoplasmic rRNA (3.8 I'g per oocyte in 38 days) and the known number of simultaneously grow ing precursor molecules in the nucleus the chain growth rate of the 40 S precursor RNA is estimated to be 34 nucleotides per second.

Lengths and patterns of transcriptional units in the amplified nucleoli of oocytes of Xenopus laevis

“…, 1969 ;Rogers and Klein , 1972 ;Bird eta !. , 1973;Scheer, 1973 ;Hagenbüchle eta!. , 1975) as weil as with estimate from electron micro copic meas urements of sp read R A molecules (Wellauer and Dawid, 1974 ;Schibier et a!., 1975).…”

“…in a pproximation the matrix unit (cf. Miller and Beatty, 1969 ;Scheer et a!. , 1973 ;see, however, also Trendelenburg et a!.…”

“…Gel Elecll'ophol'esis 0/ RNA. Lampbrush chromoso me stage oocytes were isolaled from females which had been induced to ovu late o ne day before and were incubated in Eagle's minimal essential medium ( I: I v/ v diluted wilh distilled water) contain ing a ll four lri ti ated ribonucleosides (for furthe r details see Scheer et a l. , 1975) at 23° C for 17 h. RNA was ext racted from iso lated nuc\ei as described previo usly (Scheer, 1973 ;Scheer et a l. , 1973). After the add iti o n of E. coli rRNAs (mol.…”

Ribocharin: a nuclear Mr 40,000 protein specific to precursor particles of the large ribosomal subunit

“…We have utilized vitellogenic oocytes of Xenopus laevis because they contain an extraordinarily high number of amplified prerRNA genes (Brown and Dawid , 1968) that are transcribed with nearly maximum efficiency (Miller and Beatty, 1969;8cheer et aI. , 1977), resulting in an exceedingly high net production of ribosomes (;;' 3 x 10 5 per sec ; Scheer, 1973).…”

Assembly of nuclear pore complexes mediated by major vault protein

“…Thus, the total number of nuclear pore complexes (NPCs) doubles during the interphase of HeLa cells (Maul, 1977) and increases continuously throughout the cell cycle of yeast cells (Winey et al, 1997). An especially striking example of NE enlargement is provided by Xenopus oocytes during their diplotene growth phase, when the number of NPCs increases at a rate of ~500 NPCs per minute (Scheer, 1973). Biogenesis of NPCs is considered to be a stepwise self-assembly process, beginning with a local fusion event between the inner and outer nuclear membrane, stabilization of the emerging membrane channel, and association of soluble nucleoporins or preformed nucleoporin complexes with the pore membrane in a specific order (Macaulay and Forbes, 1996;Goldberg et al, 1997;Burke and Ellenberg, 2002;Suntharalingam and Wente, 2003;Hetzer et al, 2005;Alber et al, 2007).…”