@article{c6419e19bd674ccc8168865e94e29e54,
title = "Organization of the ribosomal RNA gene cluster in the yeast Saccharomyces cerevisiae",
abstract = "The chromosomal organization of the ribosomal RNA gene cluster from Saccharomyces cerevisiae was investigated. 18 S rRNA R-loops were formed with unfractionated high molecular weight DNA crosslinked once per 2.7 × 103 bases with trioxsalen and observed in the electron microscope. Almost all the R-loops were found in very long continuous 9.34 ± 0.18 × 103 base repeating units. In addition, molecules were found at a frequency of one to two per genome equivalent of rDNA where several rRNA genes were linked to long stretches of non-rDNA. These results suggest that rDNA is arranged in a single tandem repetitive cluster of 100 to 140 genes flanked on one or both sides by non-rDNA.",
author = "Kaback, {David B.} and Norman Davidson",
note = "Funding Information: iveight than those which failed to show an rDNA satellit{\textquoteright}e in the equilibrium expev iments. It{\textquoteright} is still not clear why an rDNA satellite was not observed with high mol-c*cular weight DNA. One possibility is that the high density satellite is “t~rappcd” I)y the high molecular weight DNA. Further experiment,ation should resolve this point,. Our studies showing very long tandem rDNA molecules with very few rDNA--rron-rDNA junctions are in contrast to rDNA R-loop studies on the related yeast. S. cadsl~erge,nsi.~. which showed up to six tandem rRNA genes on a single rDh{\textquoteright}-4 molecule (Meyerinck et al., 1978). In these studies a large fraction of the R-loop-containing DNA had DNA lengths at the ends of the molecules that were larger than the sir@ rDNB t,andem repeat length. These DNA sequences were interpreted as the putative A + T-rich DNA sequences interspersed between small rRNA gene clusters (DeKlort, 1973). However, in these studies it was not clear if all the rRNS genes \v({\textquoteleft}r({\textquoteright} saturated with R-loops. In no case was the length from the most distal R-loop to 1h e (2nd of the molecules greater than the length of two rDN-4 tandem repeats, suggesting that an R-loop failed to form at{\textquoteright} a single site. Ahhough it is not clear wh> :I misqing R-loop should preferent,ially occur at the end of a DNL4 molecule. t{\textquoteright}he smwll <ample of R-loops (60) surveyed in these studies opens the possibility that this \~a{\textquoteright}: only cCncidrnt~a1. Furthermore, in some molecules these long ends could have bcc~tr due lo long single-stranded staggered ends. t,he hybrids from which, if it were thtk corrrc? USA st)rand. would not give the easily recognized R-loop structure. Altorna-liveI>-. t,lrese results could represent{\textquoteright} a fundamental differenctl between t{\textquoteright}he two yeast st.rains. It would therefore be of interest, to apply the mct)hods used in thr prescut study t)o observe high molecular weight, rDNA n~olcculrs from 8. ~o).l.~-/~f:iyertsis. During t,hesc investigations we observed what may he a replicating rDNX mol-c~culc{\~o} ntaining eight tandem genes. The molecule was arranged in an apparent “eye” form linked to a “Y” form at one end, with 18 S rRNA R-loops in both the replic*ated and unreplicated portions of the molecule (not, shown). This molecult~ was similar in struct,ure to replicating molecules ohserved for tot,al high molecular weight yeast chromosomal DNA (Petes et al., 1973). The observation suggests that ycbast rDNL5, rcplicatt~s by a similar mechanism to the bulk of the yeast chromosomal DS.4. Prior enrichment for replication structures combined uit,h R-loop labeling of the rDN .\ scqut~nccs could yield information on the Dll-,4 rcaplication of t hrse spe(Litica st{\textquoteright}qut{\textquoteright}tI{\textquoteright}:t{\textquoteright}s. TO conclude. we have used R-loop mapping to define the long range arranpemtlnt of the tandem rRNA gene sequences. The junction molecules drscriiled are what \\{\textquoteleft}t> believe to be the tirst physical evidence that rDNA is linked to norL-rDISA. {\textquoteleft}1{\textquoteright}110 nature of the DNA in the adjacent region is of interest sinccl it may t)e involvf>d in tilt, organizat,ion and the function of the nucleolus, {\textquoteleft}I{\textquoteright}ilt{\~a} lltlrors arp indebted to Rob Robinson and Mike Snyder for ttlc.ir{\textquoteright} rlsrful cornrnc~rrts and to Kathlc~c~nF lanagan for preparing tile manuscript. Tl~is work was supported t,y grants from tllc>V :llit,ed States Public Health Services (GM 10991 and GM 20927). OII({\~o} f ttlc authors (U. B. K.) was supported by t,lle Damon RunyoIl-Walter Winchell Fo~~r~tlw,ItI ~~ arld a Cnited State{\textquoteleft}s Public Health Services National Researcll Service Award. This IS ~)11-tribrltion r~rullber6 022 from the Di\+sion of Ch?mist,ry and C{\textquoteright}llernical Engilreering.",
year = "1980",
month = apr,
day = "25",
doi = "10.1016/0022-2836(80)90063-7",
language = "English (US)",
volume = "138",
pages = "745--748,IN1,749--754",
journal = "Journal of molecular biology",
issn = "0022-2836",
publisher = "Academic Press Inc.",
number = "4",
}