Nonradioactive in situ localization of poly(A)+ RNA during pollen development in anthers of tobacco (Nicotiana tabacum L.)

Summary A method is described for non-radioactive labeling of total mRNA [poly(A)+ RNA] in plastic-embedded plant tissue sections. Oligo-deoxythymidylic acid (oligo-dT) labeled with digoxigenin-conjugated dUTP was used for in situ hybridization to poly(A)+ RNA in sections of tobacco (Nicotiana tabacum) anthers. The digoxigenin was immuno-stained using antidigoxigenin IgG and gold-labeled protein-A, followed by silver enhancement of the gold label. Reproducibly similar positive staining patterns were obtained with digoxigenin-labeled oligo-dT and polyuridylic acid [poly(U)], but not with a similarly labeled sense probe, poly(A). In the developing anthers, from the onset of meiosis to the production of pollen grains, labeling patterns were compatible with a gradual depletion of nuclear and chromosome-associated sporophytic mRNA molecules during prophase of meiosis, followed by postmeiotic production of gametophytic mRNA in microspore nuclei and the vegetative nuclei of the pollen grains.Abbreviations BSA bovine serum albumin - DIG digoxigenin - IgG immunoglobulin-G - oligo-dT oligo-deoxythymidylic acid - PAS-ABB periodic acid Schiff-aniline blue black - PBS phosphate buffered saline - poly(A) polyadenylic acid - poly(U) polyuridylic acid - SSC standard saline citrate     

Release of poly a(+) messenger RNA from rat liver rough microsomes upon disassembly of bound polysomes

Several procedures were used to disassemble rat liver rough microsomes (RM) into ribosomal subunits, mRNA, and ribosome-stripped membrane vesicles in order to examine the nature of the association between the mRNA of bound polysomes and the microsomal membranes. The fate of the mRNA molecules after ribosome release was determined by measuring the amount of pulse-labeled microsomal RNA in each fraction which was retained by oligo-dT cellulose or by measuring the poly A content by hybridization to radioactive poly U. It was found that ribosomal subunits and mRNA were simultaneously released from the microsomal membranes when the ribosomes were detached by: (a) treatment with puromycin in a high salt medium containing Mg++, (b) resuspension in a high salt medium lacking Mg++, and (c) chelation of Mg++ by EDTA or pyrophosphate. Poly A-containing mRNA fragments were extensively released from RM subjected to a mild treatment with pancreatic RNase in a medium of low ionic strength. This indicates that the 3' end of the mRNA is exposed on the outer microsomal surface and is not directly bound to the membranes. Poly A segments of bound mRNA were also accessible to [(3)H] poly U for in situ hybridization in glutaraldehyde-fixed RM. Rats were treated with drugs which inhibit translation after formation of the first peptide bonds or interfere with the initiation of protein synthesis. After these treatments inactive monomeric ribosomes, as well as ribosomes bearing mRNA, remained associated with their binding sites in microsomes prepared in media of low ionic strength. However, because there were no linkages provided by nascent chains, ribosomes, and mRNA, molecules were released from the microsomal membranes without the need of puromycin, by treatment with a high salt buffer containing Mg++. Thus, both in vivo and in vitro observations are consistent with a model in which mRNA does not contribute significantly to the maintenance of the interaction between bound polysomes and endoplasmic reticulum membranes in rat liver hepatocytes.     

DNA and ribonucleotide binding characteristics of two forms of the androgen receptor from rat prostates

Androgen receptors (sedimentation value approximately 4S and Stokes radius 2.8 nm) present in the cytoplasmic fraction obtained from prostates of castrated rats bind to DNA-Sepharose and double stranded DNA. A receptor fragment (sedimentation value approximately 3S and Stokes radius 2.3 nm) obtained from rat prostates in the course of a purification procedure showed greatly diminished binding affinity for both DNA-Sepharose and soluble DNA. In contrast, both the 4S cytosol receptor and the 3S receptor form interacted with equal affinity with prostate RNA or poly(UG). These observations provide evidence that for DNA binding a different or additional part of the receptor molecule is required than for RNA and polyribonucleotide binding.     

Complementarity of sequences in low molecular weight RNAs to regions of messenger and ribosomal RNAs.

Total low molecular weight nuclear RNAs of mouse ascites cells have been labeled in vitro and used as probes to search for complementary sequences contained in nuclear or cytoplasmic RNA. From a subset of hybridizing lmw RNAs, two major species of 58,000 and 35,000 mol. wt. have been identified as mouse 5 and 5.8S ribosomal RNA. Mouse 5 and 5.8S rRNA hybridize not only to 18 and 28S rRNA, respectively, but also to nuclear and cytoplasmic poly(A+) RNA. Northern blot analysis and oligo-dT cellulose chromatography have confirmed the intermolecular base-pairing of these two small rRNA sequences to total poly(A+) RNA as well as to purified rabbit globin mRNA. 5 and 5.8S rRNA also hybridize with positive (coding) but not negative (noncoding) strands of viral RNA. Temperature melting experiments have demonstrated that their hybrid stability with mRNA sequences is comparable to that observed for the 5S:18S and 5.8S:28S hybrids. The functional significance of 5 and 5.8S rRNA base-pairing with mRNAs and larger rRNAs is unknown, but these interactions could play important coordinating roles in ribosome structure, subunit interaction, and mRNA binding during translation.     

Concentration and temperature effects in interactions of the dye pyronine G with polynucleotides

The interaction of poly(A) and poly(A).poly(U) with pyronine G dye depending on the concentration of components and temperature was studied spectrophotometrically in the visible and UV ranges at pH (6.86). It was found that the interaction of pyronine G with poly(A) and poly(A).poly(U) results in the formation of two types of complexes. The relation of the equilibrium concentrations of these complexes depends on the initial concentrations of the components in solution. The formation of complex I results in shifting the spectrum towards the short wave range with regard to the monomer band and reflects the aggregation of the dye cations. Complex II is characterized by the shift towards the long wave range. Complex II is formed in considerable amounts for poly(A).pyronine G system at large P/D and for poly(A).poly(U).pyronine G system at P/D = 5-6 and is probably due to the interaction between the dye and polynucleotides of the intercalation type or reflects the interaction between the dye and two negatively charged phosphate groups. Analysis of temperature measurements of spectra confirms the formation of various types of complexes in the system studied.     

Macrocyclic zinc(II) complexes for selective recognition of nucleobases in single- and double-stranded polynucleotides

 As an extension of our earlier discoveries that Zn^II-cyclen complex (1) (cyclen=1,4,7,10-tetraazacyclododecane) and Zn^II-acridine-pendant cyclen complex Zn^II-N-(9-acridin)ylmethyl-cyclen (3) are the first compounds to selectively recognize thymidine and uridine nucleosides in aqueous solution at physiological pH, the interaction of these and a relevant complex, bis(Zn^II-cyclen) (7), has been investigated with a series of polynucleotides, single-stranded poly(U) and poly(G), and double-stranded poly(A)·poly(U), poly(dA)·poly(dT) and poly(dG)·poly(dC). These Zn^II-cyclen complexes interact with the imide-containing nucleobases in the single-stranded poly(U), unperturbed by the presence of the anionic phosphodiester backbone. The affinity constant of 1 for each N(3)-deprotonated uracil base in poly(U) is determined to be log K= 5.1 by a kinetic measurement, which is almost the same as log K=5.2 for the interaction of 1 with uridine. Thus, they disrupt the A-U (or A-T) hydrogen bonds to unzip the duplex of poly(A)·poly(U) or poly(dA)·poly(dT), as demonstrated by lowering of the melting temperatures (T _m) of poly(A)·poly(U) and poly(dA)·poly(dT) in 5 mM Tris-HCl buffer (pH 7.6, 10 mM NaCl) with increase in their concentrations. The order of the denaturing efficiency is well correlated with that of the 1 : 1 affinity constants for each complex with uracil or thymine;7>3>1. The comparison of circular dichroism (CD) spectra for poly(A)·poly(U), poly(A), and poly(U) in the presence of 3 has revealed a structural change from poly(A)·poly(U) to two single strands, poly(A) and poly(U), caused by 3 binding exclusively to uracils in poly(U). On the other hand, the acridine-pendant cyclen complex 3, which earlier was found to associate with guanine by the Zn^II coordinating with guanine N(7), in addition to the π-π stacking, interacts with guanine in the double helix of poly(dG)·poly(dC) from outside and stabilized the double-stranded structure, as indicated by higher T _m. Received: 31 December 1997 / Accepted: 23 February 1998     

Study of salt effects on adenosine–polyuridylic acid interaction

Complex formation between poly(U) and adenosine in solutions of salts that stabilize (Na₂SO₄), destabilize (NaClO₄), or have little effect on the water structure (NaCl), as well as the poly(U)·poly(A) interaction in NaClO₄, was studied by equilibrium dialysis and uv spectroscopy. At 3°C and neutral pH, Ado·2 poly(U) is formed in 1M NaCl and 0.33M Na₂SO₄. In NaClO₄ solutions under the same conditions, an Ado·poly(U) was found over the whole range of salt concentration investigated (10 mM?1M), which has not been previously observed under any conditions. The Ado-poly(U) was also found in a NaCl/NaClO₄ mixture, the transition from the triple- to the double-helical complex occurring within a narrow range of concentration of added NaClO₄. In the presence of 1M NaCl this transition is observed on adding as little as 10 mM NaClO₄, i.e., at a [ClO]/[Cl^?] ratio of about 1:100. However, when NaClO₄ is added to a 1M solution of the stabilizing salt Na₂SO₄, no transition occurs even at a [ClO]/[SO] ratio of 1:4. Investigation of melting curves and uv spectra has shown that in an equimolar mixture of the polynucleotides, only a double-helical poly(U)·poly(A) exists in 1M NaClO₄ at low temperatures; this also holds for 1M NaCl. This changes to a triple-helical 2 poly(U)·poly(A) and then dissociates as the temperature increases. At low temperatures and the poly(U)/poly(A) concentration ratio of 2:1, a mixture of 2 poly(U)·poly(A) and poly(U)·poly(A) was observed in 1M NaClO₄, in contrast to the case of 1M NaCl. Thus, sodium perchlorate, a strong destabilizer of water structure, promotes formation of double-helical complexes both in the polynucleotide–monomer and the polynucleotide–polynucleotide systems. Beginning with a sufficiently high ionic strength (μ ? 0.9), a further increase in the salt molarity results in an increase of the poly(U)·adenosine melting temperature in both stabilizing and neutral salts and a decrease in the destabilizing salt. In Na₂SO₄ concentrations higher than 1.2M Ado·2 poly(U) precipitates at room temperature. Analysis of the binding isotherms and melting profiles of the complexes between poly(U) and adenosine according to Hill's model shows that the cooperativity of binding, due to adenosine stacking on poly(U), increases in the order NaClO₄ < NaCl < Na₂SO₄. The free energy of adenosine stacking on the template is similar to that of hydrogen bonding between adenosine and poly(U) and ranges from ?1 to ?2 kcal/mol. The values of ΔH_t [the effective enthalpy of adenosine binding to poly(U) next to an occupied site, obtained from the relationship between complex melting temperature and free monomer concentration at the midpoint of the transition] are ?14.2, ?18.3, and ?16.8 kcal/mol for 1M solutions of NaClO₄, NaCl, and Na₂SO₄, respectively. The results indicate that the effects of anions of the salts studied are related to water structure alterations rather than to their direct interaction with the complexes between poly(U) and adenosine.     

Spectroscopic study of the interaction between poly-(9-vinyladenine) and single or multistrand RNA.

The interaction between poly(9-vinyladenine) (PVAd) and poly[r(U)] was investigated by means of uv, CD, 1H-, and 31P-nmr spectroscopies. The interaction was dependent on the molecular weight of PVAd determined by uv and CD spectroscopies. Based on imino proton nmr, it was clearly found that PVAd formed the complex with poly[r(U)] by complementary hydrogen bonding. The interaction of PVAd with double- and triple-stranded helices of RNA was also investigated by uv melting behavior and 31P-nmr spectroscopy. The results suggested that PVAd could not interact with the double-stranded poly[r(A)].poly[r(U)] but did with the triple-stranded RNA.     

Formation of triple-helical nucleic acids studied by using antibodies specific for poly(A).poly(U).poly(U)

The formation of the triple helix of poly(A).poly(U).poly(U) was studied by using antibodies specific to poly(A).poly(U).poly(U). the 10-11 base chain length for oligo(A) and the 20-30 base chain length for oligo(U) may be the minimum sizes required to maintain a stable triple helix. Double-stranded poly(A).poly(U) which was the core of triple-stranded poly(A).poly(U).poly(U) could bind poly(U) and produce an analogue of poly(A).poly(U).poly(U) reactive with the antibodies even if the poly(A) or poly(U) was brominated or acetylated to the extent of 35-55%. However, brominated or acetylated poly(U) did not produce a stable triple helix with double-stranded poly(A).poly(U).     

Physical studies of the interaction of a calf thymus helix-destablizing protein with nucleic acids

UP1, a calf thymus protein that destabilizes both DNA and RNA helices, dramatically accelerates the conversion of the inactive conformers of several small RNA molecules to their biologically active forms [Karpel, R. L., Swistel, D. G., Miller, N. S., Geroch, M. E., Lu, C., & Fresco, J. R. (1974) Brookhaven Symp. Biol. 26, 165-174]. Using circular dichroic and spectrophotometric methods, we have studied the interaction of this protein with a variety of synthetic polynucleotides and yeast tRNA3Leu. As judged by perturbations in polynucleotide ellipticity or ultraviolet absorbance, the secondary structures of the single-stranded helices poly(A) and poly(C), as well as the double-stranded helices poly[d(A-T)] and poly(U.U), are largely destroyed upon interaction with UP1 at low ionic strength. This effect can be reversed by an increase in [Na+]: half the UP1-induced perturbation of the poly(A) CD spectrum is removed at 0.05 M Na+. The variation of poly(A) ellipticity and ultraviolet absorbance with [UP1]/[poly(A)]p is used to determine the length of single-stranded polynucleotide chain covered by the protein: 7 +/- 1 residues. A model is presented in which the specificity of UP1 for single strands and their concomitant distortion are a consequence of maximal binding of nucleic acid phosphates to a unique matrix of basic residues on the protein. Analogous to the effect on polynucleotides, UP1-facilitated renaturation of yeast tRNA3Leu follows the partial destruction of the inactive tRNA's secondary structure. At the tRNA absorbance maximum, UP1 effects a hyperchromic change of 10%, representing one-third of the secondary structure of the inactive conformer. This change is also clearly observable as a perturbation of the tRNA's circular dichroism spectrum.     

Interaction of ribo- and deoxyriboanalogs of yeast tRNA(Phe) anticodon arm with programmed small ribosomal subunits of Escherichia coli and rabbit liver.

A synthetic ribooligonucleotide, r(CCAGACUGm-AAGAUCUGG), corresponding to the unmodified yeast tRNA(Phe) anticodon arm is shown to bind to poly(U) programmed small ribosomal subunits of both E. coli and rabbit liver with affinity two order less than that of a natural anticodon arm. Its deoxyriboanalogs d(CCAGACTGAAGATCTGG) and d(CCAGA)r(CUGm-AAGA)d(TCTGG), are used to study the influence of sugar-phosphate modification on the interaction of tRNA with programmed small ribosomal subunits. The deoxyribooligonucleotide is shown to adopt a hairpin structure. Nevertheless, as well as oligonucleotide with deoxyriboses in stem region, it is not able to bind to 30S or 40S ribosomal subunits in the presence of ribo-(poly(U] or deoxyribo-(poly (dT) template. The deoxyribooligonucleotide also has no inhibitory effect on tRNA(Phe) binding to 30S ribosomes at 10-fold excess over tRNA. Neomycin does not influence binding of tRNA anticodon arm analogs used. Complete tRNA molecule and natural modifications of anticodon arm are considered to stabilize the arm structure needed for its interaction with a programmed ribosome.     

Interaction of N-acetyl-phenylalanyl-tRNAPhe with 70S ribosomes of Escherichia coli.

The interaction of N--Acetyl--Phe--tRNA Phe with 70 S ribosomes is a reversible process in the absence as well as in the presence of messenger. The equilibrium binding constants of these interactions were measured at different magnesium concentrations and temperatures and thermodynamical quantities computed. The enthalpy of the formation of complexes with the P site of ribosomes is larger by 6,000 cal/mol in the presence of poly (U) than in the presence of poly (C) or in total absence of messenger. Free energy differences are rather small, the association constants differ less than one order of magnitude. The association constant of N--Acetyl--Phe--tRNA Phe with the A site of ribosomes is 30--50 times lower than with the P site even in the presence of poly (U).     

Thermal stability of poly(A) and poly(U) complexes in H2O and D2O: isotopic effects on critical temperatures and transition widths.

This is a study of the effect of total and partial deuteration of solvent on critical temperatures and profiles of all four reactions occurring in poly(A) x n poly(U) (n = 1 or 2) aqueous systems. The study was done at observational times not longer than hydrogen exchange times at base pairs in helically ordered structures, and it was extended to a wide range of salt concentrations at neutral pH. The dependence of stability of polymer helical order on hydrogen mass does not appear to be merely attributable to the stronger intrahelical deuterium bonding. Substituting Deuterium for Hydrogen implies a probably predominant modulation of the entrophy term of polymer-solvent interactions. Effects of deuteration on the width of the 2(poly(A) x poly (U)) leads to poly(A) x 2poly(U)+poly(A) interconversion reaction were also observed. They bear on the role of polymer-solvent interaction on pattern recognition leading to formation of ordered structures. They also bear on the role of the same interaction on the "breathing" of ordered structures of this type.     

Interactions of poly-N6-methyladenylic acid and N6-substituted-9-methyladenines with poly-5-bromouridylic acid: a novel base-pairing

The interaction of poly-N6-methyladenylic acid (poly(m6A) with poly-5-bromouridylic acid (poly(BU) was studied by the mixing curve method. A.1 m6A: 2 BU stoichiometry was clearly indicated over a wide range of ionic strengths at neutral pH, while the binding of poly(m6A) to poly(U) is known to occur with 1 m6A:1 U. Digestion by nuclease S1 confirmed this stoichiometry, indicating the absence of single strands in a 1:2 mixture. Heating profile analysis and hydroxyapatite column chromatography provided further confirmation of this finding. To determine whether 1:2 stoichiometry holds in a monomer-polymer system, the interaction of N6-methyl-9-methyladenine (m6m9A), a corresponding monomer of poly(m6A), with poly(BU) was investigated. Equilibrium dialysis experiments showed the stoichiometry of the interaction to be 1 m6A:2 BU. Thus, we would describe some structural studies of the above complexes using c.d. and i.r. spectroscopy. Poly (m6A).2poly(BU) and m6m9A.2poly(BU) are helical and analogous to each other in structure, and the bases in the complexes are all bound by hydrogen-bonding. N6-(delta 2-isopentenyl)- and N6-allyl-9-methyladenine were also found to form complexes with poly(BU), giving similar c.d. spectra with that of m6m9A.2poly(BU). The melting experiments indicated the Tms to be substantially decreased, compared to the parent unmodified complexes, even though the Tm dependence of the polymer complex on salt concentration conforms to the typical triple strand. In the following, the biological significance of this novel pairing will be discussed.     

Biological, biochemical and physicochemical evidence for the existence of the polyadenylate - polyuridylate - poly 2'-fluoro-2'-deoxyuridylate triple-stranded complex.

The interferon-inducing activity of the double-stranded complex poly(A) - poly(U) in primary rabbit kidney cell cultures is reduced when the cells are treated with poly(dUfl) either 1 h before, simultaneously with, or 1 h after the exposure to the double-stranded complex. It has been demonstrated in experiments involving sensitivity to hydrolysis by RNAase, UV absorbance-mixing curves, and UV absorbance-temperature profiles that this phenomenon is due to the formation of the triple-stranded complex poly(A) - poly(U) - poly(dUfl). The latter complex seems to be the principal product of interactions in the following systems: poly(A) - poly(U) + poly(dUfl); poly(A) - poly(dUfl) + poly(U); and poly(A) + poly(U) + poly (dUfl).     

Adjuvant effect of poly(A:U) upon T cell-mediated in vitro cytotoxic allograft responses

The effect of complexes of polyadenylic acid and polyuridylic acid [poly(A:U)] on thymus-processed lymphocytes was studied using a tissue culture system in which T cells responded to cell bound alloantigens. The in vitro activation of T cells into cytotoxic lymphocytes was assessed with the aid of the ⁵¹Cr cytotoxic assay. Introduction of poly(A:U) into cultures or pretreatment of thymus cells prior to culture resulted in a reduction in the time required for the development of maximal cytotoxic activity as well as a reduction in the dose of allogeneic cells required for maximum stimulus. Poly(A:U) had no influence on the ability of differentiated cytotoxic T cells to lyse ⁵¹Cr-labeled target cells. The amplification of cytotoxic activity caused by poly(A:U) was specific to the antigens used to activate the thymus lymphocytes.     

Protein synthesis in yeast Saccharomyces cerevisiae. Purification of Co-eIF-2A and 'mRNA-binding factor(s)' and studies of their roles in Met-tRNAf.40S.mRNA complex formation

Antibodies prepared against a homogeneous preparation of Co-eIF-2A20 [Ahmad et al. (1985) J. Biol. Chem. 260, 6955-6959] reacted with several polypeptides including an 80-kDa polypeptide present in a crude yeast ribosomal salt wash. This 80-kDa polypeptide, containing Co-eIF-2A (Co-eIF-2A80) activity, has been extensively purified using a two-step purification procedure involving an immunoaffinity column chromatograph prepared using antibodies against Co-eIF-2A20 (fraction II) and hydroxyapatite chromatography (fraction III). The factors, eIF-2 + homogeneous Co-eIF-2A80 (fraction III) promoted Met-tRNAf.40S complex formation with an AUG codon but not with a physiological mRNA or a polyribonucleotide messenger poly(U,G) whereas eIF-2 + a partially purified Co-eIF-2A80 preparation (fraction II) promoted Met-tRNAf.40S complex formation with an AUG codon as well as with globin mRNA and poly(U,G) messenger. This factor-promoted Met-tRNAf binding to 40S ribosomes depends absolutely on the presence of a polyribonucleotide messenger containing an initiation codon (such as AUG or GUG). Other polyribonucleotide messengers tested, such as poly(U), poly(A) and poly(A,C) were completely ineffective in this binding reaction. This result indicates that the Met-tRNAf.40S.mRNA complex is formed by a direct interaction between Met-tRNAf, 40S ribosomes and the initiation site in mRNA. A mechanism has been proposed for Met-tRNAf.40S.mRNA complex formation in yeast.     

Interactions of 2-methyladenines and poly(m2A) with poly(br5U)

Mixing curve experiments and melting curve analyses have shown that poly(m2A) forms complexes with poly(br5U) with stoichiometries of either 1:1 or 1:2 in high ionic strengths. CD spectra of poly(m2A).poly(br5U) and poly(m2A).2 poly(br5U) both resemble quite well to those of poly(A). poly(br5U) and poly(A).2poly(br5U), respectively. This suggests that the corresponding complexes are closely related in the structural details. Significant similarities of the CD spectra were observed for poly(m2A).2poly(br5U) and complexes between 2,9-dimethyladenine or 2-methyladenosine and poly(br5U) in the presence of spermine, indicating also the 1:2 stoichiometry. Thus, a methyl group at the position 2 of adenine ring is not necessarily hindering a formation of the Watson-Crick type base pairings.     

Base specificity in the interaction of ethidium with synthetic polyribonucleotides.

Base specificity in the interaction of ethidium with double stranded synthetic RNA homopolymers has been studied by means of spectroscopic (UV-visible absorption and fluorescence), microcalorimetric and dilatometric techniques. The results show a strong base specificity in this interaction, the association constant with poly A:poly U being more than three order of magnitude higher than with poly O:poly C. The interaction is mainly enthalpy driven, the differences in affinity being essentially entropic in origin. These evidences along with the dilatometric data suggest that the observed base specificity may arise from the different extent of water release upon intercalation.     

Thermodynamics of single-stranded RNA binding to oligolysines containing tryptophan.

The equilibrium binding to the synthetic RNA poly(U) of a series of oligolysines containing one, two, or three tryptophans has been examined as a function of pH, monovalent salt concentration (MX), temperature, and Mg2+. Oligopeptides containing lysine (K) and tryptophan (W) of the type KWKp-NH2 and KWKp-CO2 (p = 1-8), as well as peptides containing additional tryptophans or glycines, were studied by monitoring the quenching of the peptide tryptophan fluorescence upon binding poly(U). Equilibrium association constants, K(obs), and the thermodynamic quantities delta G(o)obs, delta H(o)obs, and delta S(o)obs describing peptide-poly(U) binding were measured as well as their dependences on monovalent salt concentration, temperature, and pH. In all cases, K(obs) decreases significantly with increasing monovalent salt concentration, with (delta log K(obs)/delta log [K+]) = -0.74 (+/- 0.04)z, independent of temperature and salt concentration, where z is the net positive charge on the peptide. The origin of these salt effects is entropic, consistent with the release of counterions from the poly(U) upon formation of the complex. Upon extrapolation to 1 M K+, the value of delta G(o)obs is observed to be near zero for all oligolysines binding to poly(U), supporting the conclusion that these complexes are stabilized at lower salt concentrations due to the increase in entropy accompanying the release of monovalent counterions from the poly(U). Only the net peptide charge appears to influence the thermodynamics of these interactions, since no effects of peptide charge distribution were observed. The binding of poly(U) to the monotryptophan peptides displays interesting behavior as a function of the peptide charge. The extent of tryptophan fluorescence quenching, Qmax, is dependent upon the peptide charge for z less than or equal to +4, and the value of Qmax correlates with z-dependent changes in delta H(o)obs and delta S(o)obs(1 M K+), whereas for z greater than or equal to +4, Qmax, delta H(o)obs, and delta S(o)obs (1 M K+) are constant. The correlation between Qmax and delta H(o)obs and delta S(o)obs(1 M K+) suggests a context (peptide charge)-dependence of the interaction of the peptide tryptophan with poly(U). However the interaction of the peptide tryptophan does not contribute substantially to delta G(o)obs for any of the peptides, independent of z, due to enthalpy-entropy compensations. Each of the tryptophans in multiple Trp-containing peptides appear to bind to poly(U) independently, with delta H(o)Trp = -2.9 +/- 0.7, although delta G(o)Trp is near zero due to enthalpy-entropy compensations.(ABSTRACT TRUNCATED AT 400 WORDS)