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channel. These proteins are buried into the phospholipid bilayer (Hayashimoto
et al.
1990
). NPCs can act as the semipermeable gate, which allows easy passage
to small molecules; however, they restrict the movement of larger molecules. The
molecules can overcome this barrier by having a nuclear localization sequence
(NLS) which can be recognized by the protein named importins, which can be
transported through the pores into the nucleus on the expense of energy (O
Neill
et al.
1993
). Actually, it is not clear how DNA alone or with nanoparticles is
transported into the nucleus. One of the reasons may be that DNA-loaded
nanoparticles may recognize the surface and get attached to the surface of the
nuclear membrane, where the import in molecule can transfer the DNA into the
nucleus. In this case, a nanoparticle protects DNA from nucleases until it gets into
the nucleus. On this basis, several nanoparticles can be used to conjugate with
nucleic acids for their proper transfer into the living cell (Ito et al.
1983
), and
various types of nanoparticles have been used as nucleic acid carriers (Ruzin and
McCarthy
1986
). The nanoparticles have some advantages over other methods as
they are not subject to microbial attack, can be easily synthesized, are less toxic, and
exhibit a good stability (Hoffmann-Tsay et al.
1994
). Many scientists successfully
adopted different nanoparticulate delivery carriers like polymeric nanoparticle,
metallic nanoparticle, and quantum dots in gene therapy (Jun et al.
2008
; Akhter
et al.
2011
). Nanoparticles play an important role as a gene carrier in biotransfor-
mation process, as well as protection of DNA damage from ultrasound as reported
by Liu et al. (
2008
). Many scientists used green fluorescent protein (GFP) tagged
with nanoparticles to demonstrate its effectiveness and reported that nanoparticles
alone enter into the cytoplasm as seen in the green cytoplasmic content (Jun
et al.
2008
).
The GFP has been extensively studied in recent years, with various types and
variants. GFP was first noticed in jellyfish,
Aequorea victoria
, in 1961. GFP is a
compact, globular, acidic, 27-kDa molecule with stability at the greater range of pH
from 5 to 9 (Chalfie et al.
1994
). Santos et al. (
2007
) have reported the X-ray
crystallographic analysis of the GFP revealing the presence of a
'
-barrel structure in
which the fluorophore is buried in the protein interior. Amino acids Serine, tyrosine,
and glycine form the fluorophore of GFP wild type, and these amino acids in
recombinant GFP had two reactions, autocatalytic cyclization between the carbonyl
of Tyr 66 and the amino group of Gly 67 and the carbonyl of Ser 65 and Tyr
66 amino group, giving rise to a covalent bond and oxygen-dependent slow step,
where the single bond between the carbons C
β
Tyr66 results in the conjugated
double bonds with fluorescent properties (Chalfie and Kain
1998
). Recently, several
mutants with emission at higher wavelength have been described with both
enhanced fluorescence and rapid expression as compared to that of wild-type
GFP, thereby increasing their sensitivity and applicability over wild-type GFP
(Robey et al.
1998
; Doi and Yanagawa
1999
). Wild-type and mutant forms of
GFP have been widely used as reporters of gene expression. Their small size, the
limited or no effect upon cell physiology when expressed, and their stability coupled
with their ability to maintain their intrinsic fluorescence when attached to other
peptides or proteins have made them an essential part of molecular biology research.
ʱ
-C
β
