Zinc fingers are a ubiquitous class of protein domain with considerable variation in structure and function. The FCS-type zinc finger is a highly diverged group of C2-C2 zinc finger which is present in animals, prokaryotes and viruses, but not in plants. It is named after the conserved phenylalanine and serine residues associated with the third cysteine. The FCS-type zinc finger is a structurally diverse family which accommodate both nucleic-protein and protein-protein interaction zinc fingers. The FCS-Like Zinc finger (FLZ) domain is a plant specific domain found in all taxa except algae. FLZ domain containing proteins are bryophytic in origin and this protein family is expanded in higher plants. Although the molecular functions of the FLZ protein family members in general are not well understood, many of the members are attributed to plant growth and development, stress mitigation, sugar signaling and senescence. The FLZ-type zinc finger is likely to be involved in protein-protein interaction [1, 2, 3].

The FLZ-type zinc finger is predicted to form an alpha-beta-alpha secondary structure composed of an N-terminal short alpha-helix, a beta hairpin followed by a longer C-terminal alpha helix. Four highly conserved cysteine residues in the FLZ-type zinc finger are believed to bind zinc in a tetrahedral coordination [4, 4].

Some proteins known to contain a FLZ-type zinc finger are listed below [4]:

• Arabidopsis thaliana MEDIATOR OF ABA-REGULATED DORMANCY 1 (MARD1) or FLZ9, involved in absissic acid (ABA)-mediated seed dormancy and induced during senescence.
• Arabidopsis thaliana INCREASED RESISTANCE TO MYZUS PERSICAE (IRM1) or FLZ4, constitutive overexpression of IRM1 results in mechanical barriers that make it difficult for M. persicae to reach the phloem and subsequently reduces its population size.
• Wheat salt related hypothetical protein (TaSRHP), overexpression of TaSHRP results in enhanced resistance to salt and drought stress.

1. A novel zinc-finger protein with a proline-rich domain mediates ABA-regulated seed dormancy in Arabidopsis. Plant Mol. Biol. 54, 1-9
2. DUF581 Is Plant Specific FCS-Like Zinc Finger Involved in Protein-Protein Interaction. PLoS ONE 9, e99074
3. Comprehensive Evolutionary and Expression Analysis of FCS-Like Zinc finger Gene Family Yields Insights into Their Origin, Expansion and Divergence. PLoS ONE 10, e0134328
4. Expression of Arabidopsis FCS-Like Zinc finger genes is differentially regulated by sugars, cellular energy level, and abiotic stress. Front Plant Sci 6, 746

Zinc fingers are a ubiquitous class of protein domain with considerable variation in structure an
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