Biochimica et Biophysica Acta, 1049 (1990) 339-342 339 Elsevier BBAEXP 90181 BBA Report Interactions of berberine with poly(A) and tRNA R. Nandi, D. Debnath and M. Maiti Indian Institute of Chemical Biology, Calcutta (India) (Received 4 August 1989) (Revised manuscript received 2 April 1990) Key words: Berberine; Poly(A); tRNA; Alkaloid-nucleic acid interaction The interaction of berberine chloride with poly(A) and tRNA has been studied by various spectroscopic techniques. Binding parameters determined from spectrophotometric and spectrofluorimetric measurements by Scatchard analysis indicate a very high effective binding capacity of berberine to poly(A) as compared to DNA or tRNA. The circular dichroism studies show that binding of berberine to poly(A) causes a significant change in the circular dichroic spectrum of poly(A) itself, as manifested by (i) a decrease of both positive and negative bands and (ii) appearance of a conservative type of extrinsic circular dichroic spectrum in the wavelength range of 300-400 nm, while it does not cause any significant alteration to the A form structure of tRNA. It is concluded that berberine interacts stronger with poly (A) than DNA or tRNA. The results are interpreted in terms of its reported biological activities. Berberine chloride, a benzodioxolo-benzoquinolizine alkaloid, exhibits antitumour, antibacterial and antimi- crobial activities [1,2]. It has been reported to be useful in the treatment of dermal leishmaniasis, gastroenteritis in children and cholera diseases [1]. The DNA binding properties of this alkaloid have been studied in consid- erable detail [3-6]. Recently, we have shown that berberine exhibits considerable specificity towards alter- nating AT polymer and its isoquinoline moiety binds to AT-rich DNA by a mechanism of intercalation [6]. It is known that both mRNA-poly(A) and tRNA play an important role in the process of gene expression in cells [7,8]. Polyadenylation of primary transcripts is required for the maturation of most eukaryotic mRNAs and the poly(A) tail is thought to confer stability of the mRNA molecule [9]. Furthermore the polyadenylation process plays a regulatory role, in gene expression, in the production of alternative forms of protein [10,11]. Although various results on the complex formation between berberine and DNA have been reported, very little is known about how it interacts with poly(A) and tRNA. The present study describes some physico- chemical aspects of its interaction with poly(A) and tRNA. The results are also compared with the Abbreviation: CD, circular dichroism. Correspondence: M. Maiti, Scientist, Indian Institute of Chemical Biology, Calcutta 700 032, India. 0167-4781/90/$03.50 © 1990 Elsevier Science Publishers B.V. (Biomedical berberine-DNA complex formation under identical con- ditions. Calf thymus DNA (Type I), Escherichia coli strain W tRNA (type XX), poly(A) and berberine chloride were purchased from Sigma (U.S.A.). The concentrations of nucleic acids, in terms of nucleotide phosphate were determined spectrophotometrically using extinction coefficient (c) at the indicated wavelengths (nm): calf thymus DNA (6600 M- 1. cm- l, 260); poly(A) (10 000 M -1- cm -1, 257); and tRNA (72000 M -1. cm -1, 260). The concentration of berberine was determined spectro- photometrically using an c of 225000 M -1.cm -1 at 344 nm. Absorbance and fluorescence spectra of either berberine alone or mixed with polynucleotides were obtained at 22°C using a Shimadzu UV-260 automatic recording spectrophotometer and a Shimadzu spectro- fluorimeter RF-540 equipped with recorder DR-3, re- spectively, according to methods described earlier [5,6,12-14]. Circular dichroic (CD) spectra of poly- nucleotides and their complexes with berberine were conducted on a Jasco J-20A spectropolarimeter at- tached with a data processor, model J-DPY as stated earlier [15]. The effect of progressively increasing the concentra- tions of poly(A) on the absorption spectrum of berberine was studied (data not shown). The binding of berberine was characterized by bathochromism and hypochro- mism in the absorption bands. The series of spectra exhibited three sharp isosbestic points at 358, 377 and Division)