.:...31_2------SCIENTIFIC CORRESPONDENCE------N-AT_u_R_E_v_oL_._33_7_26.:...JA...:.:N...:.:U...:.:A~R..:..:.Y..:..:.19=H9 muscle-type acetylcholine receptor'. We have found that both cell lines contain an RNP in maize protein N-ras gene that is activated by a point fp SIR-We wish to point out an interesting mutation at the third base of codon 61 feature in the sequence of the abscisic and, in new cell stocks obtained directly 0.1 acid-induced glycine-rich protein (AAIP) from the American Type Culture Collec­ of maize recently reported by Gomez et tion, that the majority of marker chromo­ al. '. The protein contains a sequence (see somes are common to the cell lines. below) which conforms perfectly to the Furthermore, DNA fingerprinting with RNP consensus sequence'-4 that has been locus-specific and core probes fails to 20 30 40 found so far in heterogenous nuclear reveal differences between the two lines. Period P(Myrl RNA-, messenger RNA-, pre-ribosomal Both cell lines were derived in the same Fourier spectra of two long-term reversal func­ RNA-, and small-nuclear RNA-binding laboratory but RD was described" and tions plotted against period P = 2:n:/w. R~ (r, proteins. submitted to the A TCC before the first r,), from ref. 1, is shown as a solid curve, and R~(T) (equation (3)) as a dash-dotted line. The MaizeAAIP: report of TE671. When considered 49 straight dashed line is the exact asymptotic 56 together these observations indicate that ... Arg Gly Phe Gly Phe Val Thr Phe ... envelope for P< < T to both spectra. TE671 is most probably a subline of the RNP consensus sequence: rhabdomyosarcoma cell line RD. tinuities (of size Ad, taken to have the 1 ... Lys Gly Phe Gly Phe Val Thr Phe ... M.R. STRATTON value 5 Myr- , and separation T = r,- r,) Arg Tyr Ala Tyr X Tyr B.R. REEVES but carries no information on variations in C.S. COOPER between. The spectrum of this function, This strongly suggests that AAIP is a Chester Beatty Laboratories, single-stranded nucleic-acid binding pro­ Institute of Cancer Research, R~(T) = N-'A,d (P/:n:) I sin (:n:T/ P) I (3) tein, most probably an RNA-binding pro­ Fulham Road, London SW3 6JB, UK is compared in the figure with that of lL(t) tein (RNP). Several other features of the obtained by Lutz and Watson'. (Here N is AAIP sequence also resemble those found 1. McAllister, R. eta/. Int. J. Cancer20, 206-212 (1977). in some of these proteins. The protein 2. Dewhurst, K. eta/. FEBS Lett. 213,138-143 (1987). the total number of reversals.) We inter­ 3. Clapham, P.R. eta/. Nature 337,368-370 (1988). pret the close correspondence in shape, appears to contain two distinct domains: 4. Stratton, M.R. eta/. Carcinogenesis (in the press). an amino-terminal domain (about 90 5. Schoepfer, R. eta/. FEBS Lett. 226, 235-240(1988). position and peak heights as verification 6. McAllister eta/. Cancer 24, 520-526 (1969). of our initial claim. The straight dashed amino acids) that contains the RNP con­ line denotes the exact smali-P asymptotic sensus sequence, and a carboxy-terminal envelope for any function l(t) that has glycine-rich domain. The amino-terminal Spectral peaks the same discontinuities as l~(t) and domain is the putative RNA-binding SIR-Lutz and Watson 1 discuss the fre­ l\(t). The positions of the maxima of domain'. There are extensive similarities quency spectrum of the Harland et at. 2 R~(T) are given by P" = Tl(n+ 1/2) for in the general character of the amino­ geomagnetic reversal record of the past integers n ~ 0; for all T, they agree well terminal domain with that of the putative 165 million years. This spectrum has been with the values from the numerical RNA-binding domain of several RNP interpreted as showing a 30-million-year Fourier transform of lL(t) given in Table proteins'. A glycine-rich domain is also a short-term oscillation superimposed on an 1 of ref. 1, for which r, was varied in feature of some RNP proteins (for exam­ aperiodic long-term variation. Lutz and discrete steps. Therefore, the grouping ple, the hnRNP protein A1 (ref. 5), and Watson argue that the long-term com­ together there of peak positions with more the nucleolar protein nucleolin"). AAIP ponent, lL(t), dominates the frequency or less constant period is arbitrary. When may be the first plant protein described so spectrum for periods P up to 40 million r, - r, decreases continuously, the peak far to contain an RNP consensus sequence. years. Here I show that the spectrum in positions do so too. The predicted property of AAIP as an this range is essentially determined by the The influence of short-term oscillations RNA-binding protein can be readily strong boundary discontinuities intro­ would thus be seen only as noticeable tested, for example, by chromatography duced by performing a Fourier transform deviations of the peak heights from those on small-subunit DNA columns, on ribo­ homopolymer columns, and by photo­ lL(t) over a finite interval (r10 r,); that of R~(T), that is, from the envelope of Rr chemical crosslinking to RNA. is, these discontinuities dominate over any ( r 10 r,). Using a Poisson process, Lutz time variation of l~(t) between r, and r,. and Watson' show that the long-term Abscisic acid is a hormone that appears The influence of discontinuities component alone may generate fluctua­ to modulate the response of plants to becomes apparent when the limits of the tions in the peak heights that are large adverse conditions, and it seems to also Fourier transform are extended to (- oo, enough to account for the spectrum of the play a role in embryogenesis. Determin­ + oo). This leaves all integrals unchanged, total reversal function l(t). ing if AAIP is indeed an RNA-binding provided that the 'extended' function Thus, for periods >S 40 Myr, the spec­ protein, and if so, what RNA it binds to l;(t) has the form trum Re ( r,, r,) of the total reversal should be important for understanding the function is determined mainly by the mechanism of these important processes. ERIKA MoRTENSON A.~.(t)forr, ~ t~ r 2 strong discontinuities in lL(t) at r, and A.;(t) = r,, and hides any information on short­ GIDEON DREYFUSS { 0 otherwise (1) term variations. These can be reliably Department of Biochemistry, detected in the spectrum only if the dis­ Molecular Biology and Cell Biology,

As A1 (t) is largest at the boundaries, continuous long-term variation can be Northwestern University, lL(t) exhibits large discontinuities there. subtracted before the Fourier transform Evanston, Illinois 60208, USA The dominance of these discontinuities operation. 1. Gomez, J. eta/. Nature334, 262-264 (1988). 2. Adam, S.A., Nakagawa, T., Swanson, M.S .. Woodruff, can be demonstrated by considering a RAINER LIEBMANN T.K. & Dreyfuss, G. Malec. cell. Bioi. 6. 2932-2943 (1986). simplified trial function AEG Aktiengesellschaft, 3. Swanson, M.S., Nakagawa, T.Y., LeVan, K. & Dreyfuss, Sedanstrasse 10, G. Malec cell. Bioi. 7, 1731-1739 (1987). Act = constant for - T/2 ~ t ~ T/2 4. Dreyfuss, G., Swanson, M.S. & Pirl.ol-Roma, S. Trends D-7900 Ulm, FRG hiochem. Sci. 13,86-91 (1988). A.~(t) = { 5. Cobianchi, F., SenGupta, D.N., Zmudzka, B.Z. & Wilson, 0 otherwise (2) I. Lutz, T.M. & Watson, G.S. Nature 334, 24(}-242 (1988). S.H. J. bioi. Chern. 261, 3536-3543 (1986). 2. Harland, W .B. eta!. A Geological Time Scale (Cambridge 6. Lapcyre. B .. Bourbon, H. & Amalric. F. Proc. natn. A cad. which retains the two boundary discon- University Press. 19R2). Sci. U.S.A. 84, 1819-1823 (1987).