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2.6.1. Marker genes that confer resistance to antibiotics
2.6.1.1. kpt (or aplr
IV)
gene
The hpr gene codes for the enzyme hygromycin phosphotransfernse (HPT;
E.C. 2.7.1.1 19) also known as anlinoglycoside 4-'phosphotransferase (APH[4]). This
gene was isolated from E. coli and it confers resistance to the antibiotic hygromycin B
(van den Elzen et al., 1985). When hygromycin occupies the ribosomal binding site of
the elongation factor 2 (EF-2) in prokaryote cells consequently. the elongation of
polypeptide chain is inhibited and protein synthesis interrupted, causing the same
symptoms described for the other aminoglycoside antibiotics (Benveniste and Davies.
1973).
2.6.1.2.
nptII
(or neo) gene
The nptll (or neo) gene was isolated from the transposon Tn5 of E. coli and it
encodes for the enzyme neomycin phosphotransferase
I1 (NPT
11;
E.C. 2.7.1.95). also
known as aminoglycoside 3'phosphotransferase I1 (APH[3]II) (Bevan et al., 1983;
Fraley et a[., 1983, Herrera-Estrella e r al.. 1983). The active aminoglycoside
antibiotic inhibits the protein synthesis in prokaryotic cells, by binding to the 30s
subunit of the ribosome, blocking the formation of initiation complexes and
decreasing the fidelity of translation. In plant cells, these antibiotics exert its effect on
mitochondria and chloroplasts, acting in the same manner by impairing protein
synthesis. These organelles have ribosome that are similar to those found in bacteria
and are also susceptible to aminoglycoside antibiotics. Therefore, in the presence of
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