METHODS: A Companion to Methods in Enzymology 15, 1–2 (1998)Article No. ME980600

EDITORIAL

RNA editing is a process by which the informa- was discovered a year later, is apolipoprotein (apo)B mRNA editing in mammals (7, 8). Another 2tional content of an RNA is altered cotranscrip-

tionally or posttranscriptionally, such that its cod- years later, a simple assay for apoB mRNA editingwas described by Driscoll et al. (9). The techniqueing specificity is changed by a process other than

splicing. A number of reviews on RNA editing have allowed the degree of editing to be assayed easily;similar procedures have since been adopted by in-been published (1–3), and one book on the subject

was published in 1993 (4); another comprehensive vestigators involved in other RNA editing systems.Because it is a well-known technique that has beenbook on RNA modification and editing is currently

in press (5). However, none of these publications well described (9, 10), I have decided not to includeit here. Instead, I have included one paper (Smith)deals with the practical aspects of RNA editing

research. In this issue I have brought together a on apoB mRNA editing that deals with methods ofthe analysis of the editosome complex and anotherpanel of experts who present some practical hints

and methods on research in RNA editing. In doing article (Chang and Chan) on the evolutionary anal-ysis of RNA editing enzymes.so, I have been fortunate to have investigators

from many different research disciplines discuss ApoB mRNA editing is mediated by a multicom-ponent editosome complex (11). Apobec-1, the cat-their approach, because RNA editing encompasses

many different mechanisms involving diverse or- alytic subunit of the complex, is the only compo-nent that has been cloned and shown to beganisms.

Two articles in this issue cover RNA editing in essential for editing. It is clear, however, that apo-bec-1 works in concert with other protein compo-kinetoplastids. RNA editing was first described in

the kinetoplast of trypansomes in 1986, when Be- nents, and the macromolecular structure that cat-alyzes apoB mRNA in situ has been called annne et al. (6) noted the presence of four uridines

in the mitochondrial transcript for cytochrome-c editosome. The analysis of the structure of theeditosome complex is one of the most excitingoxidase subunit 2 of trypansomes that are not en-

coded in the DNA. Since its first description, nu- areas of research in apoB mRNA editing. The edi-tosome is not a simple static structure, and RNAmerous examples of RNA editing in the form of U-

insertion and U-deletion occurring posttranscrip- editing may be controlled by dynamic interactionsbetween, and the selective assembly and disas-tionally have been observed in kinetoplastids. The

paper by Stuart et al. in this issue describes meth- sembly of, the various components of the edito-some complex. Smith reviews the methods thatods in this system dealing with the mechanism and

the molecular components involved. The emphasis have been applied to the study of the structureand function of apoB mRNA editosomes.is on in vitro editing systems. The paper by Sabat-

ini et al. describes the biochemical methods used Four years after C r U editing in apoB mRNAwas described, A r I editing, involving the mRNAsin analyzing RNA editing in kinetoplastid mito-

chondria. These two papers will help the novice for glutamate-activated receptor channel sub-units, was discovered (12). The description of ain the field get started in investigations in RNA

editing in kinetoplastids. double-stranded RNA unwindase activity had ac-tually preceded the recognition that the same en-Being the first example of RNA editing de-

scribed, kinetoplastid RNA editing is also the best zyme, which has adenosine deaminase activity,seems to be responsible for A r I editing. A majorstudied. The next example of RNA editing, which

11046-2023/98 $25.00Copyright q 1998 by Academic PressAll rights of reproduction in any form reserved.

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2 EDITORIAL

breakthrough in that area was the purification and lar in vitro systems are being investigated inother laboratories dealing with mitochondrialcloning of some of the enzymes responsible, nowRNA editing. A similar in vitro system is notknown as double-stranded RNA-specific adenosineavailable for chloroplasts. However, in this case,deaminases (dsADARs). In this issue, O’Connell etconsiderable insight into the editing mechanismal. describe the purification and expression of thecan be gleaned from an in vivo approach. BockADAR1 and ADAR2 isoforms. Other examples ofdetails the use of chloroplast transformation forA r I editing are being described with increasingstudying plastid RNA editing in the last paper offrequency. Interestingly, the enzymes involved,this issue.the dsADARs, show homology to apobec-1, which

has cytidine deaminase activity. Both types of en-zymes contain zinc-coordinating motifs that arealso found in some other deaminases. Thus, the REFERENCESstructure of these enzymes may provide a clue tothe evolutionary origin of RNA editing. Chang and 1. Chan, L. (1993) BioEssays 15, 33–41.Chan describe the methods that can be applied to 2. Bass, B. L. (1993) in The RNA World (Gesteland, R. F., and

Atkins, J. F. Eds.), p. 383, Cold Spring Harbor Laboratorythe analysis of the rate of evolution of the RNAPress, New York.editing enzymes and to the construction of a phylo-

3. Smith, H. C., Gott, J. M., and Hanson, M. R. (1997) RNA 3,genetic tree of the RNA editing enzymes and other1105–1123.related deaminases.

4. Benne, R. (1993) RNA Editing: The Alteration of Protein Cod-RNA editing is a widely distributed phenome- ing Sequences of RNA, Ellis Horwood, Chichester, England.

non among living organisms. It is seen in animals 5. Grosjean, H., and Benne, R. (in press) Modification and Edit-as well as in plants. Research on single-base sub- ing of RNA, ASM Press, Washington, DC.stitution RNA editing in plants is at a much ear- 6. Benne, R., van den Burg, J., Brakenhoff, J. P., Sloof, P., Van

Boom, J. H., and Tromp, M. C. (1986) Cell 46, 819–816.lier stage than that in mammals, even though ed-7. Powell, L. M., Wallis, S. C., Pease, R. J., Edwards, Y. H.,iting in mitochondrial and chloroplastid

Knott, T. J., and Scott, J. (1987) Cell 50, 831–840.transcripts in plants appears to be more wide-8. Chen, S.-H., Habib, G., Yang, C.-Y., Gu, Z.-W., Lee, B.R.,spread and extensive than editing in nuclear tran-

Weng, S.-A., Silberman, S. R., Cai, S.-J., Deslypere, J. P., Ros-scripts in mammals. One reason for the relatively seneu, M., Gotto, A. M., Jr., Li, W.-H., and Chan, L. (1987)slow progress in RNA editing research in plants Science 238, 363–366.is the apparent difficulty in applying to these or- 9. Driscoll, D. M., Wynne, J. K., Wallis, S. C., and Scott, J.

(1989) Cell 58, 519–525.ganisms some of the methods that have been suc-10. Chan, L., and Teng, B.-B. (1996) in Methods in Molecularcessfully used in mammals and protozoans. There

Genetics (Adolph, K. W. Ed.), pp. 335–347, Academic Press,are, however, some important advances thatOrlando, FL.

should greatly facilitate research in plants in the11. Chan, L., Chang, B. H.-J., Nakamuta, M., Li, W.-H., and

future. The development of a pea in vitro system Smith, L. C. (1997) Biochim. Biophys. Acta 1345, 11–26.for studying RNA editing of mitochondrial tran- 12. Sommer, B., Kohler, M., Sprengel, R., and Seeburg, P. H.

(1991) Cell 67, 11–19.scripts is described in the paper by Yu et al. Simi-

Lawrence ChanGuest Editor

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