Frameshifting

The conversion of a functional into a pseudogene most frequently results from mutations such as frameshift mutations or deletions. Even though pseudogenes might still have some retained functionality such as promoter-or enhancer-like features, they are usually classified as pseudogenes upon their lack of protein-coding ability. 

Lesch-Nyhan syndrome, an overproduction hyperuricemia characterized by frequent episodes of uric acid hthiasis and a bizarre syndrome of self-mutilation, reflects a defect in hypoxanthme-guanine phosphoribo-syl transferase, an enzyme of purine salvage (Figure 34—4). The accompanying rise in intracellular PRPP results in purine overproduction. Mutations that decrease or abohsh hypoxanthine-guanine phosphoribosyltrans-ferase activity include deletions, frameshift mutations, base substitutions, and aberrant mRNA splicing. 

Frameshift Mutations Result From Deletion or Insertion of Nucleotides in DNA That Generates Altered mRNAs... 

P-Thalassemla (MIM 141900) A very wide variety of mutations in the p-globin gene, including deletions, nonsense and frameshift mutations, and others affecting every aspect of its structure (eg, splice sites, promoter mutants)... 

Resistance to certain antibiotics can arise as a consequence of mutations to chromosomal genes because of changes in the DNA sequence. Mutations can occin due to single base pair changes. Transitions involve the substitution of one purine (A or G) for another and therefore one pyrimidine (C or T) for another. Transversions involve a change from a pyrimidine to a purine and vice versa. Frameshift mutations occin when one or... 

More extensive changes in the DNA sequence (often referred to as macrolesions) can also occur. Deletions result in the loss of part of the DNA sequence. Insertions add extra base pairs to a gene. Transversions occur when a segment ofthe DNA is reversed and duplications occur when a segment ofthe DNA is repeated. Some ofthese changes also result in frameshifts. 

Finally, Santiago et al. (47) demonstrated that lymphocyte chemoattraction induced by rheumatoid arthritis synovial fluid is independent of CCR5. They showed that T cells from individuals with CCR5 delta 32 mutation (a 32-base-pair frameshift deletion resulting in absent CCR5 expression) migrate normally to chemokines present in the synovial fluids of RA patients (47). 

Studies have led to the identification of 14 alleles associated with PFK deficiency. Eight missense mutations, one nonsense mutation, one frameshift muta-... 

Hereditary deficiency of LDH-B was first reported by Kitamura et al. in 1970 (K21). Since then, this enzyme deficiency has been discovered in at least five families in Japan. There were no clinical symptoms in these cases. On the other hand, LDH-A deficiency was associated with an exertional rhabdomyolysis and myoglobinuria after severe exercise (K15). One Japanese and one Italian with LDH-A deficiency showed the typical skin rash. To date, nine LDH-A variants have been analyzed at the molecular level, and four missense mutations, one nonsense mutation, one frameshift mutation due to a single base insertion, and three gene deletions have been elucidated (K16, M5). Missense mutations have also been identified in LDH-B deficiency (M6). 

Acatalasemia is a rare hereditary deficiency of tissue catalase and is inherited as an autosomal recessive trait (03). This enzyme deficiency was discovered in 1948 by Takahara and Miyamoto (Tl). Two different types of acatalasemia can be distinguished clinically and biochemically. The severe form, Japanese-type acatalasemia, is characterized by nearly total loss of catalase activity in the red blood cells and is often associated with an ulcerating lesion of the oral cavity. The asymptomatic Swiss-type acatalasemia is characterized by residual catalase activity with aberrant biochemical properties. In four unrelated families with Japanese-type acatalasemia, a splicing mutation due to a G-to-A transition at the fifth nucleotide in intron 4 was elucidated (K20, W5). We have also determined a single base deletion resulting in the frameshift and premature translational termination in the Japanese patient (HI6). 

Lamhonwah AM, Tein I. Carnitine uptake defect frameshift mutations in the human plasmalemmal carnitine transporter gene. Biochem Biophys Res Commun 1998 252(2) 396-401. 

The mutagenicity of benzofa]pyrene for bacteria was demonstrated by Ames et al. (60) They found that in the presence of rat liver homogenates benzo[a]pyrene induced both frameshift and base-pair substitution mutations. When the chemistry of benzo[a]pyrene activation had been worked out and the ultimate carcinogenic form identified as a diolepoxide, BPDE (reviewed in 61-62), several investigators (63-66) showed that BPDE was an extremely potent mutagen, also capable of inducing both frameshift and base-pair substitution mutations. 

We have not directly determined the relative frequencies of frameshift mutations and other mutational events in comparison to the base substitution mutations. However, based on the high frequency of nonsense mutations (11%) among all lacl mutants induced by BPDE and because nonsense mutations are monitorable at less than one-fifth of the lacl codons and, even then, only via certain base pair substitutions, we believe that base substitutions account for a major fraction of mutations induced by BPDE. 

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