Recent studies

Such observations as above have spurred an extensive research into "Junk DNA" in recent
years, some of which is briefly presented below.

Various important roles of "Junk DNA" have been discovered in recent years.
In June 2004 a team at Harvard Medical School (HMS) reported, that they have, in a yeast,
found a "Junk DNA" gene that regulates the activity of nearby genes. While common genes
work by giving rise to proteins, this gene works by just being switched on. Then it blocks the
activity of an adjacent gene.

Quote: "In a region of DNA long considered a genetic wasteland, HMS
researchers have discovered a new class of gene."... "The researchers have
evidence that the new gene, SRG1, works by physically blocking transcription
of the adjacent gene, SER3. They found that transcription of SRG1 prevents the
binding of a critical piece of SER3's transcriptional machinery." Source: "Junk
DNA Yields New Kind of Gene", Focus, Harvard Medical School, June 4 2004.
Some studies have found that noncoding DNA plays a vital role in the regulation of gene
expression during development (Ting SJ. 1995. A binary model of repetitive DNA sequence
in Caenorhabditis elegans. DNA Cell Biol. 14: 83-85.), including:

• Development of photoreceptor cells (Vandendries ER, Johnson D, Reinke R. 1996.
Orthodenticle is required for photoreceptor cell development in the Drosophila eye.
Dev Biol 173: 243-255.),
• The reproductive tract (Keplinger BL, Rabetoy AL, Cavener DR. 1996. A somatic
reproductive organ enhancer complex activates expression in both the developing
and the mature Drosophila reproductive tract. Dev Biol 180: 311-323.), and
• The central nervous system (Kohler J, Schafer-Preuss S, Buttgereit D. 1996. Related
enhancers in the intron of the beta1 tubulin gene of Drosophila melanogaster are
essential for maternal and CNS-specific expression during embryogenesis. Nucleic
Acids Res 24: 2543-2550.).
Over 700 studies have demonstrated the role of non-coding DNA as enhancers for
transcription of proximal genes. This includes a/o:
• Eosinophil-derived neurotoxin (EDN) and eosinophil cationic protein (ECP) (Tiffany
HL, Handen JS, Rosenberg HF. 1996. Enhanced expression of the eosinophil-derived
neurotoxin ribonuclease (RNS2) gene requires interaction between the promoter
and intron. J Biol Chem 271: 12387-12393),
• The variable region of the rearranged immunoglobulin mu (IgM) gene (Jenuwein T,
Forrester WC, Fernandez-Herrero LA, Laible G, Dull M, Grosschedl R. 1997. Extension
of chromatin accessibility by nuclear matrix attachment regions. Nature 385: 269-
272.; Nikolajczyk BS, Nelsen B, Sen R. 1996. Precise alignment of sites required for
mu enhancer activation in B cells. Mol Cell Biol 16: 4544-4554),
• The alpha-globin gene (Bouhassira EE, Kielman MF, Gilman J, Fabry MF, Suzuka S,
Leone O, Gikas E, Bernini LF, Nagel RL. 1997. Properties of the mouse alpha-globin
HS-26: relationship to HS-40, the major enhancer of human alpha-globin gene
expression. Am J Hematol 54: 30-39),
• The activin beta A subunit gene (Tanimoto K, Yoshida E, Mita S, Nibu Y, Murakami K,
Fukamizu A. 1996. Human activin betaA gene. Identification of novel 5' exon,
functional promoter, and enhancers. J Biol Chem 271: 32760-32769).
Over 60 studies have demonstrated the role of non-coding DNA as silencers for suppression
of transcription of proximal genes. Such silencer genes include a/o:
• Apolipoprotein A-II gene (Bossu JP, Chartier FL, Fruchart JC, Auwerx J, Staels B, Laine
B. 1996. Two regulatory elements of similar structure and placed in tandem account
for the repressive activity of the first intron of the human apolipoprotein A-II gene.
Biochem J 318: 547-553.),
• The osteocalcin gene (Goto K, Heymont JL, Klein-Nulend J, Kronenberg HM, Demay
MB. 1996. Identification of an osteoblastic silencer element in the first intron of the
rat osteocalcin gene. Biochemistry 35: 11005-11011),
• The 2-crystallin gene (Dirks RP, Kraft HJ, Van Genesen ST, Klok EJ, Pfundt R,
Schoenmakers JG, Lubsen NH. 1996. The cooperation between two silencers creates
an enhancer element that controls both the lens-preferred and the differentiation
stage-specific expression of the rat beta B2-crystallin gene. Eur J Biochem 239: 23-
32).
Some studies indicate that non-coding DNA regulates translation of proteins. This includes
a/o.
• The Lipoprotein Lipase gene (Ranganathan G, Vu D, Kern PA. 1997. Translational
Regulation of Lipoprotein Lipase by Epinephrine Involves a Trans-acting Binding
Protein Interacting with the 3' Untranslated Region. J Biol Chem 272: 2515-2519)
• Glutathione peroxidase and phospholipid-hydroperoxide glutathione peroxidase
genes (Bermano G, Arthur JR, Hesketh JE. 1996. Role of the 3' untranslated region in
the regulation of cytosolic glutathione peroxidase and phospholipid-hydroperoxide
glutathione peroxidase gene expression by selenium supply. Biochem J 320: 891-
895),
• The luteinizing hormone/human chorionic gonadotropin receptor gene (58. Lu DL,
Menon KM. 1996. 3' untranslated region-mediated regulation of luteinizing
hormone/human chorionic gonadotropin receptor expression. Biochemistry 35:
12347-12353),
• The thyrotropin receptor gene (Kakinuma A, Chazenbalk G, Filetti S, McLachlan SM,
Rapoport B. 1996. BOTH the 5' and 3' noncoding regions of the thyrotropin receptor
messenger ribonucleic acid influence the level of receptor protein expression in
transfected mammalian cells. Endocrinology 137: 2664-2669),
• The interleukin 1 type I receptor gene (Ye K, Vannier E, Clark BD, Sims JE, Dinarello
CA. 1996. Three distinct promoters direct transcription of different 5' untranslated
regions of the human interleukin 1 type I receptor:
a possible mechanism for control
of translation. Cytokine 8: 421-429)