Structural Modification Strategies, Interfacial Charge-Carrier Dynamics, and Solar Energy Conversion Applications of Organic-Inorganic Halide Perovskite Photocatalysts

Over the past few decades, organic-inorganic halide perovskites (OIHPs) as novel photocatalyst materials have attracted intensive attention for an impressive variety of photocatalytic applications due to their excellent photophysical (chemical) properties. Regarding practical application and future commercialization, the air-water stability and photocatalytic performance of OIHPs need to be further improved. Accordingly, studying modification strategies and interfacial interaction mechanisms is crucial. In this review, the current progress in the development and photocatalytic fundamentals of OIHPs is summarized. Furthermore, the structural modification strategies of OIHPs, including dimensionality control, heterojunction design, encapsulation techniques, and so on for the enhancement of charge-carrier transfer and the enlargement of long-term stability, are elucidated. Subsequently, the interfacial mechanisms and charge-carrier dynamics of OIHPs during the photocatalytic process are systematically specified and classified via diverse photophysical and electrochemical characterization methods, such as time-resolved photoluminescence measurements, ultrafast transient absorption spectroscopy, electrochemical impedance spectroscopy measurements, transient photocurrent densities, and so forth. Eventually, various photocatalytic applications of OIHPs, including hydrogen evolution, CO2 reduction, pollutant degradation, and photocatalytic conversion of organic matter.

Unravelling the Interfacial Dynamics of Bandgap Funneling in Bismuth-Based Halide Perovskites

An environmentally friendly mixed-halide perovskite MA₃ Bi₂ Cl_{9- x} I_x with a bandgap funnel structure has been developed. However, the dynamic interfacial interactions of bandgap funneling in MA₃ Bi₂ Cl_{9- x} I_x perovskites in the photoelectrochemical (PEC) system remain ambiguous. In light of this, single- and mixed-halide lead-free bismuth-based hybrid perovskites-MA₃ Bi₂ Cl_{9- y} I_y and MA₃ Bi₂ I₉ (named MBCl-I and MBI)-in the presence and absence of the bandgap funnel structure, respectively, are prepared. Using temperature-dependent transient photoluminescence and electrochemical voltammetric techniques, the photophysical and (photo)electrochemical phenomena of solid-solid and solid-liquid interfaces for MBCl-I and MBI halide perovskites are therefore confirmed. Concerning the mixed-halide hybrid perovskites MBCl-I with a bandgap funnel structure, stronger electronic coupling arising from an enhanced overlap of electronic wavefunctions results in more efficient exciton transport. Besides, MBCl-I's effective diffusion coefficient and electron-transfer rate demonstrate efficient heterogeneous charge transfer at the solid-liquid interface, generating improved photoelectrochemical hydrogen production. Consequently, this combination of photophysical and electrochemical techniques opens up an avenue to explore the intrinsic and interfacial properties of semiconductor materials for elucidating the correlation between material characterization and device performance.

Mixed-Dimensional van der Waals Heterostructure for High-Performance and Air-Stable Perovskite Nanowire Photodetectors

An organic-inorganic hybrid perovskite nanowire (NW), CH₃NH₃PbI₃, shows great potential for high-performance photodetectors due to its excellent photoresponse. However, the inefficient carrier collection between the one-dimensional (1D) NWs and metallic electrodes, as well as degradation of the perovskite, limits the viability of the CH₃NH₃PbI₃ NWs for commercial production. Here, we demonstrate a photodetector with a mixed-dimensional van der Waals heterostructure of hexagonal boron nitride (hBN)/graphene (Gr)/1D CH₃NH₃PbI₃, which exhibits excellent responsivity and specific detectivity of up to 558 A/W and 2.3 × 10¹² Jones, owing to the improved carrier extraction at the electrical contact between Gr and the NW. As for the atomic encapsulation of hBN, the device is extremely robust and maintains its outstanding performance for more than 2 months when exposed to air. Moreover, benefitting from the 1D geometry of the CH₃NH₃PbI₃ NW, our device is highly sensitive to polarized light. The mixed-dimensional van der Waals heterostructure, hBN/Gr/1D CH₃NH₃PbI₃, would provide a novel idea and protocol for fabricating high-performance and air-stable photoelectronic devices based on organic-inorganic hybrid perovskite NWs.

Bandgap Funneling in Bismuth-Based Hybrid Perovskite Photocatalyst with Efficient Visible-Light-Driven Hydrogen Evolution

The photocatalytic system using hydrohalic acid (HX) for hydrogen production is a promising strategy to generate clean and renewable fuels as well as value-added chemicals (such as X₂ /X₃ ^- ). However, it is still challenging to develop a visible-light active and strong-acid resistive photocatalyst. Hybrid perovskites have been recognized as a potential photocatalyst for photovoltaic HX splitting. Herein, a novel environmentally friendly mixed halide perovskite MA₃ Bi₂ Cl_9-x I_x with a bandgap funnel structure is developed, i.e., confirmed by energy dispersive X-ray analysis and density functional theory calculations. Due to gradient neutral formation energy within iodine-doped MA₃ Bi₂ Cl₉ , the concentration of iodide element decreases from the surface to the interior across the MA₃ Bi₂ Cl_9-x I_x perovskite. Because of the aligned energy levels of iodide/chloride-mixed MA₃ Bi₂ Cl_9-x I_x , a graded bandgap funnel structure is therefore formed, leading to the promotion of photoinduced charge transfer from the interior to the surface for efficient photocatalytic redox reaction. As a result, the hydrogen generation rate of the optimized MA₃ Bi₂ Cl_9-x I_x is enhanced up to ≈341 ± 61.7 µmol h^-1 with a Pt co-catalyst under visible light irradiation.

Idiopathic Internal Thoracic Artery (ITA) Pseudoaneurysm treated with Endovascular Embolization

A 44-year-old female was diagnosed with an ITA pseudoaneurysm in the right supraclavicular fossa. She was successfully treated with endovascular embolization. The challenges of diagnosis and treatment are discussed.

RNA Conformational Sampling: II. Arbitrary Length Multinucleotide Loop Closure

In this paper, we describe how the inverse kinematic solution to the loop closure problem may be generalized to reclose a RNA segment of arbitrary length containing any number of nucleotides without disturbing the atomic positions of the rest of the molecule. This generalization is made possible by representing the boundary conditions of the closure in terms of a set of virtual coordinates called RETO, allowing the inverse kinematics to be reduced from the original six-variable/six-constraint problem to a four-variable/four-constraint problem. Based on this generalized closure solution, a new Monte Carlo algorithm has been formulated and implemented in a fully atomistic RNA simulation capable of moving loops of arbitrary lengths using torsion angle updates exclusively. Combined with other conventional Monte Carlo moves, this new algorithm is able to sample large-scale RNA chain conformations much more efficiently. The utility of this new class of Monte Carlo moves in generating large-loop conformational rearrangements is demonstrated in the simulated unfolding of the full-length hammerhead ribozyme with a bound substrate.

The sign problem in real-time path integral simulations: using the cumulant action to implement multilevel blocking

A practical method to tackle the sign problem in real-time path integral simulations is proposed based on the multilevel blocking idea. The formulation is made possible by using a cumulant expansion of the action, which in addition to addressing the sign problem, provides an unbiased estimator for the action from a statistically noisy sample of real-time paths. The cumulant formulation also allows the analytical gradients of the action to be computed with little extra computational effort, and it can easily be implemented in a massively parallel environment.

RNA conformational sampling. I. Single-nucleotide loop closure

We consider the loop-closure problem for nucleic acids and describe an efficient numerical algorithm for closing single-nucleotide loops in nucleic acids. Using six new internal coordinates to represent the nucleotide conformation, which we call the R-representation, the original closure problem with six free torsion angles in each nucleotide can be reduced to one with only four degrees of freedom. Simple numerical techniques have been used to solve the resulting loop-closure equations, and a test of the closure algorithm on a set of RNAs consisting of more than 7000 nucleotides was able to regenerate the native torsion angles in every nucleotide in the test set without exception. We show how the conformational probability density transforms when the original torsion angle representation is mapped onto the new R-representation. We also present statistical evidence showing that the delta and nu(2) torsion angles are coupled, and how this coupling affects the conformation probability density in the R-representation. In addition to the backbone, the same loop-closure algorithm can also be applied to close the ribose ring. The algorithm is freely available at http://tyrosine.use.edu/closure.

Reverse monte carlo method and its implications for generalized cluster algorithms

We describe a novel switching algorithm based on a "reverse" Monte Carlo method, in which the potential is stochastically modified before the system configuration is moved. This new algorithm facilitates a generalized formulation of cluster-type Monte Carlo methods, and the generalization makes it possible to derive cluster algorithms for systems with both discrete and continuous degrees of freedom. The roughening transition in the sine-Gordon model has been studied with this method, and high-accuracy simulations for system sizes up to 1024(2) were carried out to examine the logarithmic divergence of the surface roughness above the transition temperature, revealing clear evidence for universal scaling of the Kosterlitz-Thouless type.

Heat-inducible translationally controlled tumor protein of Trichinella pseudospiralis: cloning and regulation of gene expression

To elucidate the mechanism of inducing translationally controlled tumor protein (TCTP) in stress adaptation of adenophorean nematodes, the complete coding sequence of TCTP of the infective-stage larvae of Trichinella pseudospiralis was characterized. Two cDNA clones with different 3' untranslated region were identified. Tp-TCTP contained an open reading frame of 534 bp encoding 177 residues. The gene with five introns was expressed as histidine-tagged fusion protein having a molecular mass of 17.5 kDa. Quantitative reverse transcriptase polymerase chain reaction (RT-PCR) analysis showed that TCTP RNA was not accumulated when the infective-stage larvae were heat-shocked for 1 h at 45 or 60 degrees C. Using enzyme-linked immunosorbent assay and antiserum against the fusion protein, the expression of TCTP was found to be up-regulated at the translational level. The data suggest that translational regulation of TCTP may play an important role in the early heat-stress adaptation of the trichinellid. Cluster analysis demonstrated that the TCTP sequence of T. pseudospiralis is closely related to that of T. spiralis, but is diverged from the secernentean species.

Large-scale simulations of the two-dimensional melting of hard disks

Large-scale computer simulations with more than four million particles have been performed to study the melting transition in a two-dimensional hard disk fluid. The van der Waals loop previously observed in the pressure-density relationship of smaller simulations is shown to disappear systematically with increase in sample size, but even with these large system sizes, the freezing transition still exhibits what appears to be weakly first-order behavior, though the scaling of the bond orientation order is consistent with the Halperin-Nelson-Young picture. Above this freezing transition region, scaling analysis of the translational order yields a lower bound for the melting density that is much higher than previously thought and provides compelling evidence that the solid phase first melts into a hexatic phase via a continuous transition, before it goes into the isotropic phase.

Cloning and characterization of the Cu/Zn superoxide dismutase of Trichinella pseudospiralis

Copper/zinc (Cu/Zn) superoxide dismutase (SOD) activity was identified for the first time in both crude somatic extracts (CE) and excretory/secretory (E/S) products of Trichinella pseudospiralis. It was the dominant SOD in infective-stage larvae. Native polyacrylamide gel electrophoresis of CE and E/S products yielded a prominent band, which was cyanide-sensitive and was partly inhibited by hydrogen peroxide in SOD assay. Cytosolic Cu/Zn SOD was cloned. The 471-bp full-length cDNA sequence contained an open reading frame of 157 amino acids. The gene contained three introns. Quantitative reverse transcription-polymerase chain reaction indicated that the expression of cytosolic Cu/Zn SOD was substantially higher in infective-stage larvae than in adult worms. Cluster analysis showed that the sequence of the Cu/Zn SOD of T. pseudospiralis, an adenophorean nematode, is related to those of Brugia pahangi, Acanthocheilonema viteae, Onchocerca volvulus, and Haemonchus contortus (all belonging to the sercenentean group).

Stochastic potential switching algorithm for Monte Carlo simulations of complex systems

This paper describes a new Monte Carlo method based on a novel stochastic potential switching algorithm. This algorithm enables the equilibrium properties of a system with potential V to be computed using a Monte Carlo simulation for a system with a possibly less complex stochastically altered potential V. By proper choices of the stochastic switching and transition probabilities, it is shown that detailed balance can be strictly maintained with respect to the original potential V. The validity of the method is illustrated with a simple one-dimensional example. The method is then generalized to multidimensional systems with any additive potential, providing a framework for the design of more efficient algorithms to simulate complex systems. A near-critical Lennard-Jones fluid with more than 20,000 particles is used to illustrate the method. The new algorithm produced a much smaller dynamic scaling exponent compared to the Metropolis method and improved sampling efficiency by over an order of magnitude.

Superfluidity in CH4-doped H2 nanoclusters

We report a theoretical study of superfluidity in CH(4)-doped para-H(2) nanoclusters. Path integral simulations for clusters of 12-16 H(2) around a single CH(4) molecule were carried out at temperatures between 0.5 and 2 K to study the superfluid response of the cluster. The results indicate that a rapid increase in the superfluid response is expected to occur around 1 K. We analyzed the structures and statistics of these clusters and found that the larger permutation cycles which dominate the superfluid component tend to adopt ringlike structures on the surface of the CH(4) molecule.

Cloning and characterization of the mitochondrial heat-shock protein 60 gene of Trichinella spiralis

The full-length cDNA of mitochondrial heat-shock protein (hsp) 60 of the infective-stage larva of Trichinella spiralis was cloned by degenerative PCR and rapid amplification of cDNA end reactions. The 1,945 bp full-length cDNA sequence contained an open reading frame of 576 amino acids. A mitochondrial signal peptide was located at the N-terminal and a GGM motif at the C-terminal. The gene contained ten exons and nine introns. RT-PCR analysis indicated that thermal, cold, acidic and oxidative treatment did not elicit significant changes in the expression of mitochondrial hsp 60 in the larvae. Cluster analysis showed that the sequence of the hsp 60 gene of T. spiralis is closely related to that of Drosophila melanogaster.

Characterization and cloning of metallo-proteinase in the excretory/secretory products of the infective-stage larva of Trichinella spiralis

Inhibitor sensitivity assays using azocaesin and FTC-caesin as substrates showed that the excretory/secretory (E/S) products of the infective-stage larvae of Trichinella spiralis contained serine, metallo-, cysteine and aspartic proteinases. The activity of the metallo-proteinase was zinc ion dependent (within a range of ZnSO(4) concentrations). Gelatin-substrate gel electrophoresis revealed two bands of molecular mass 48 and 58 kDa which were sensitive to the metallo-proteinase inhibitor EDTA. The former peptide was probably a cleavage product of the latter. The authenticity of the 58 kDa metallo-proteinase as an E/S product was confirmed by immunoprecipitation. Using PCR and RACE reactions, a complete nucleotide sequence of the metallo-proteinase gene was obtained. It comprised 2,223 bp with an open reading frame encoding 604 amino acid residues. The 3' untranslated region consisted of 352 bp, including a polyadenylation signal AATAA. A consensus catalytic zinc-binding motif was present. The conserved domains suggest that the cloned metallo-proteinase belongs to the astacin family and occurs as a single copy gene with 11 introns and 10 exons. Cluster analysis showed that the sequence of the metallo-proteinase gene of T. spiralis resembles those of Caenorhabdites elegans and Strongyloides stercoralis.

Identification of some heat-induced genes of Trichinella spiralis

Three heat-induced genes of the infective-stage larvae of Trichinella spiralis were successfully identified by the suppression subtractive hybridization (SSH) technique. As indicated by reverse Northern blotting, 19 of 25 clones were scored as differentially transcribed in the heat-shocked infective-stage larvae. The sequencing data showed the presence of 12 different genes. Three were homologous to histone H3, histone H2B and translationally controlled tumour protein (TCTP). A 0.6 kb cDNA of histone H3 was generated by the RACE method and sequenced. It contained an open reading frame of 136 amino acids that demonstrated 94% identity with genes from Drosophila hydei. Semi-quantitative RT-PCR indicated that after heat-shock treatment, the expression levels of histone H3, histone H2B and TCTP increased 4.8, 27 and 5.7-fold, respectively. Northern analysis confirmed the upregulation of histone H3, histone H2B and TCTP transcripts. The upregulation of these genes during stress conditions has not been reported in parasitic organisms. The stress proteins may play an active role to sustain the parasite after exposure to hostile host factors.

DNA-binding activity in the excretory-secretory products of Trichinella pseudospiralis (Nematoda: Trichinelloidea)

A novel DNA-binding peptide of Mr approximately 30 kDa was documented for the first time in the excretory-secretory (E-S) products of the infective-stage larvae of Trichinella pseudospiralis. Larvae recovered from muscles of infected mice were maintained for 48 h in DMEM medium. E-S products of worms extracted from the medium were analysed for DNA-binding activity by the electrophoretic mobility shift assay (EMSA). Multiple DNA-protein complexes were detected. A comparison of the Mr of proteins in the complexes indicated that they could bind to the target DNA as a dimer, tetramer or multiples of tetramers. Site selection and competition analysis showed that the binding has a low specificity. A (G/C-rich)-gap-(G/T-rich)-DNA sequence pattern was extracted from a pool of degenerate PCR fragments binding to the E-S products. Results of immunoprecipitation and electrophoretic mobility supershift assay confirmed the authenticity of the DNA-binding protein as an E-S product.

Single-stranded endonuclease activity in the excretory--secretory products of Trichinella spiralis and Trichinella pseudospiralis

A novel acidic extracellular single-stranded endonuclease was demonstrated for the first time in the excretory-secretory (E-S) products of 2 species of Trichinella. Unlike the double-stranded endonuclease reported earlier, the single-stranded molecule is divalent cation independent and is detected in both T. spiralis and T. pseudospiralis E-S products. It hydrolysed single-stranded DNA and RNA at comparable rates. The single-stranded endonuclease was sensitive to inhibition by Zn2+ and to high concentrations of NaCl. Zymographic analysis indicated that it was encoded by at least 3 peptides of Mr approximately 50-60 kDa. The rate of hydrolysis of single-stranded targets by the E-S products was substantially higher than that of the double-stranded molecule. Due to the differences in peptide profile, divalent cation dependence, and species-specific expression, the single and double-stranded endonucleases are likely to be encoded by different proteins and may have different functions.

Path-integral Monte Carlo simulations without the sign problem: multilevel blocking approach for effective actions

The multilevel blocking algorithm recently proposed as a possible solution to the sign problem in path-integral Monte Carlo simulations has been extended to systems with long-ranged interactions along the Trotter direction. As an application, results for the real-time quantum dynamics of the spin-boson model are presented.

Characterization of endonuclease activity from excretory/secretory products of a parasitic nematode, Trichinella spiralis

Double-stranded endonuclease activity was demonstrated for the first time in the excretory/secretory (ES) products of a parasitic nematode, Trichinella spiralis, which can reorganize host muscle cells. The endonuclease introduced double-stranded breaks to the native DNA. The ES double-stranded endonuclease(s) was sequence nonspecific, with a pH optimum below 6, and required divalent cations as a cofactor. Its activity was inhibited by the Zn2+ ion. It was detected mainly in the ES products of the infective-stage larvae of T. spiralis collected at 37 degrees C and was present in much smaller amounts in samples collected at 43 degrees C and in the products of T. pseudospiralis, a nonencapsulated species. The activity of endonuclease was blocked by antibodies against ES products. Zymographic analysis showed that the endonuclease activity was associated with at least three molecular forms, designated approximately 25, 30 and 58 kDa, respectively.

Regulation by phosphorylation of the zinc finger protein KRC that binds the kappaB motif and V(D)J recombination signal sequences

The DNA binding protein KRC (forkappaB binding andrecognitioncomponent of the V(D)J recombination signal sequence) belongs to a family of large zinc finger proteins that bind to the kappaB motif and contains two widely separated DNA binding structures. In addition to the kappaB motif, KRC fusion proteins bind to the signal sequences of V(D)J recombination to form highly ordered complexes. Here, we report that KRC may be regulated by post-translational modifications. Specific protein kinases present in the nucleus of pre-B cells phosphorylated a KRC fusion protein at tyrosine and serine residues. Such protein modifications increased DNA binding, thereby providing a mechanism by which KRC responds to signal transduction pathways. KRC is a substrate of epidermal growth factor receptor kinase and P34cdc2 kinase in vitro. Our results suggest that activation of the KRC family of transcription factors may provide a mechanism by which oncogenic tyrosine kinases regulate genes with kappaB-controlled gene regulatory elements.

KRC transcripts: identification of an unusual alternative splicing event

Mouse KRC is a large zinc finger protein that binds to the kappaB motif of gene transcription and to the recognition signal sequences for the somatic recombination of the immunoglobulin and T-cell receptor gene segments. The mouse KRC gene is more than 70 kilobases (kb) in size, and contains at least seven exons, with the largest transcript being approximately 9.5 kb. Multiple differentially spliced transcripts of KRC were identified in thymus and brain, which would result in the production of multiple KRC protein isoforms with different N-termini and number of DNA binding domains. Alternative splicing events leading to the production of these multiple transcripts have been elucidated. Of particular interest are the exclusions in some transcripts of sequences from a gigantic exon of 5487 base pairs (bp), or from an exon of 176 bp. Both potentially deleted exons code for zinc finger motifs that are essential components of the N-terminal and C-terminal DNA binding domains, respectively. Another intriguing phenomenon found in some KRC transcripts is the skipping of a 459 bp fragment within the gigantic exon that would code for the N-terminal DNA binding domain. Bacterial fusion proteins derived from this fragment bind specifically to KRC target DNAs. Apparently, distinct alternative splicing events could eliminate the N-terminal DNA binding domain of KRC.

The mouse DNA binding protein Rc for the kappa B motif of transcription and for the V(D)J recombination signal sequences contains composite DNA-protein interaction domains and belongs to a new family of large transcriptional proteins

Rc is a DNA binding protein with dual specificities for the V(D)J recombination signal sequences and for the B motif of the immunoglobulin kappa chain gene enhancer. The largest Rc transcript present in lymphoid cells/tissues is approximately 9 kb. Molecular cloning and sequence determination for 8822 bp of mouse Rc cDNA revealed an open reading frame of 2282 amino acids and long 5'- and 3'-untranslated regions. The derived amino acid sequence contains multiple DNA and protein interaction domains. Composite ZAS structures with tandem zinc fingers, an acidic motif, and a Ser/Thr-rich segment are located near the N-terminal and the C-terminal regions. The middle region of Rc contains a lone zinc finger, an acidic motif, a Ser-rich region, a nucleus localization signal, and GTPase motifs. Cloning and characterization of a mouse Rc gene show that the Rc cDNA corresponds to seven exons located in a genomic region spanning 70 kb. Exon 2 is exceptionally large, with 5487 bp. cDNA cloning and Northern blot analyses revealed multiple Rc transcripts, probably generated by alternative splicings. Sequence comparisons show that Rc belongs to a ZAS protein family that is involved in gene transcription and/or DNA recombination. The major histocompatibility complex class I gene enhancer binding proteins MBP1 and MBP2 are other representatives of this ZAS protein family.

The V(D)J recombination signal sequence and kappa B binding protein Rc binds DNA as dimers and forms multimeric structures with its DNA ligands

The murine DNA binding protein Rc binds to the heptamer motif of the V(D)J recombination signal sequences and to the kappa B motif of the immunoglobulin enhancer. Bacterial fusion proteins for Rc and DNA ligands of Rc form multiple protein-DNA complexes in electrophoretic mobility shift assays (EMSA). Large complexes formation is favored by an increased Rc concentration. In order to determine the architecture of these complexes, the apparent molecular weights of the protein-DNA complexes were first determined by their gel mobilities. The data suggest that Rc binds to its DNA ligands as dimers, tetramers, and multiples of tetramers. The inference that Rc binds DNA as dimers was substantiated by the formation of chimeric complexes when two electrophoretically distinguishable Rc proteins were employed in EMSA. Methylation interference experiments show that there are no contiguous protein binding sites evident in the DNA of the larger complexes. Apparently, multimerization occurs via protein-protein interactions. Such interaction was demonstrated by the formation of Rc dimers and tetramers in a chemical crosslinking experiment. Significantly, the multimerization of DNA-bound Rc could be involved in bringing the variable region gene segments together for the somatic V(D)J recombination.

Molecular cloning of a zinc finger protein which binds to the heptamer of the signal sequence for V(D)J recombination

The somatic V(D)J recombination for the assembly of the Ig and TCR genes is mediated by the recombination signal sequences (Rss) and the V(D)J recombinase. A cDNA clone was isolated from a lambda gt11 expression library made from mouse thymocyte poly(A)+ RNA, using the Rss as a ligand. The deduced amino acid sequence of the putative protein, designated Recognition component (Rc), reveals a pair of Cys2-His2 zinc fingers followed by a Glu- and Asp-rich acidic domain. In addition, there are five copies of the Ser/Thr-Pro-X-Arg/Lys sequence, which are putative DNA binding units. The zinc finger-acidic domain structures present in Rc are also found in several enhancer binding proteins, such as those for the kappa B motif of the Ig kappa light chain enhancer or related sequences. Bacterial fusion proteins for Rc bind preferentially to the Rss heptamer and to the kappa B motif. The dual affinities of Rc for the Rss heptamer and the kappa B motif suggest a possible link between Ig transcription and somatic recombination. The formation of multiple 'gel-shifted' DNA-protein complexes for Rc and its DNA ligand suggests that these complexes tend to multimerize.