Zinc finger proteins are generally thought of as DNA-binding transcription factors. An increasing number of mutations have been described that affect genes encoding components of the post-transcriptional machinery. In particular, multifunctional proteins that link transcription with post-transcriptional processes have been implicated in several human diseases including cancer. A predominant feature of these proteins is the zinc finger, an ancient structural motif that mediates protein ratio protein interactions and is capable of interacting with both DNA and RNA. Zinc finger proteins are the most abundant class of proteins in the human proteome, yet the majority remain uncharacterized. Here we describe multifunctional zinc finger proteins linked to human development and disease. The examples discussed are WT1, ZNF74, EWS, TLS, TAFII68, YY1, CTCF and the GLI proteins.
C2H2 zinc finger proteins make up one of the largest protein families in eukaryotic organisms. Recent study in several different systems has identified a set of novel zinc finger proteins that appear to form a distinct subfamily that we have named the NET family. C2H2 zinc finger proteins make up one of the largest protein families in eukaryotic organisms. Recent study in several different systems has identified a set of novel zinc finger proteins that appear to form a distinct subfamily that we have named the NET family.
TFIIIA-type zinc fingers have been found in a number of eucaryotic transcription factors as DNA-binding motifs. In plants, as many as 30 proteins have been reported that have either one, two, three or four zinc fingers. Plant zinc-finger proteins are characterized by long spacers of diverse lengths between adjacent fingers and a highly conserved sequence, QALGGH, located within a putative DNA-contacting surface of each finger. In vitro DNA-binding experiments with two-fingered proteins of petunia have revealed that these proteins bind to target DNA sequences in a manner that is distinctive from that of their animal counterparts: (1) they specifically recognize the spacing between two core sites in target DNA, (2) they have a unique base-determinant position. Regulatory functions have been assigned to some of the TFIIIA-type zinc finger proteins in Arabidopsis, petunia and chinese cabbage.
The Cys(2)His(2) zinc finger is one of the most common DNA-binding motifs in Eukaryota. A simple mode of DNA recognition by the Cys(2)His(2) zinc finger domain provides an ideal scaffold for designing proteins with novel sequence specificities. The ability to bind specifically to virtually any DNA sequence combined with the potential of fusing them with effector domains has led to the technology of engineering of chimeric DNA-modifying enzymes and transcription factors. This in turn has opened the possibility of using the engineered zinc finger-based factors as novel human therapeutics. One such synthetic factor-designer zinc finger transcription activator of the vascular endothelial growth factor A gene has recently entered clinical trials to evaluate the ability of stimulating the growth of blood vessels in treating the peripheral arterial obstructive disease.
Abiotic stresses are important factors affecting plant growth and development and limiting agricultural production worldwide. Plants have evolved complex regulatory mechanisms to respond and adapt to constantly changing environmental conditions. C2H2 zinc finger proteins form a relatively large family of transcriptional regulators in plants. Recent studies have revealed that C2H2 zinc finger proteins function as key transcriptional regulators in plant responses to a wide spectrum of stress conditions, including extreme temperatures, salinity, drought, oxidative stress, excessive light and silique shattering.
Certain classes of zinc finger proteins, such as CCCH zinc finger proteins, often function as RNA-binding proteins and regulate RNA metabolism4. CCCH zinc finger proteins are characterized by one or more CCCH zinc finger domains containing three cysteines and a histidine. Nearly 60 CCCH zinc finger proteins have been identified in humans and mice. Although the functions of most CCCH zinc finger proteins remain obscure, emerging evidence suggests that some CCCH zinc finger proteins are involved in a broad range of biological processes that are associated with immune responses, including cytokine production, immune cell activation, immune homeostasis and antiviral innate immunity, as well as in regulation of cell differentiation and cancer cell growth.
Zinc-finger nucleases are emerging as very powerful tools for directed genome modifications. Their key features are: a DNA-binding domain comprised of zinc fingers that can be designed to favor very specific targets; a nonspecific cleavage domain that must dimerize to cut DNA--this requirement enhances specificity and minimizes random cleavage. ZFNs have been shown to be effective in a wide range of organisms and cell types.
Designed zinc-finger (ZnF) proteins can recognize AT base pairs by H-bonds in the major groove, which are disrupted, if the adenine base is methylated at the N6 position. Based on this principle, researchers recently designed a ZnF protein, which does not bind to DNA, if its recognition site is methylated.